Noob Question: Is It safe to send newborn photos through WhatsApp? If it's not, why?

Noob answer? No, because the other party will likely store them in unsafe manner and send it through Facebook Messenger to that Aunt of theirs.

As far as anyone knows WhatsApp uses secure end to end encryption. So only your device and the other person's device has access to the picture.
The only downside is that WhatsApp is a closed source program, so it isn't verifiable that the encryption is correctly implemented.
- Also, even now, your message could be thousand times encrypted - Google drive backups are not. At least by default. Don't know anything about iOS, but probably same.
  
  iOS WhatsApp backups can also be E2E encrypted, but I don't believe it's on by default.

First off, it sounds like congratulations are in order! A new life is always cause for celebration! I hope you, your spouse and your new child are doing well.
Short answer to your question: NO! DO NOT SEND ANY SENSITIVE DATA (INCLUDING PHOTOS) VIA ANY PATH, OR SERVICE YOU DO NOT FULLY CONTROL!!!
Long answer: While What'sApp, Meta and the like, are not known to be quite as... proactive as Google in cracking down on child pornography there is the very real risk that any data you send via any service may be scanned via a ML algorithm and flagged. What happens next depends on the particular service. Not sure about WhatsApp, but in the case of Google, once your account is flagged, your entire account is forwarded to Law Enforcement. As you are just sending pictures of your new arrival (Congrats again!), odds are that the officer assigned will take one look at it and clear you. All good, so far, right? Yea, not so much. You might not be going to jail but when Google locks down an account, they do not reactivate it, regardless of what law enforcement might decide, and as they are a private company, suing them to get your accounts reactivated is a lost cause. They are allowed to decide whom they want as a customer so long as their standard is applied evenly and doesn't target certain protected groups.
No service you use should ever be allowed to see anything important to you. Ever.
If you can, I would self host a cloud service like NextCloud out of your own home to share files freely, although an GPG encrypted email would work. Your current email provider is fine, although use a third party email client that supports encryption, like Thunderbird. and much as I like ProtonMail's stance on privacy, I would still use a separate encryption method for anything truly sensitive.
I know I sound like a privacy nutjob, but seriously. When the consequences of a false allegation are that high, you should recognize the threat and act accordingly. I use Google, TikTok, iCloud and others, but if the subject matter is anything much more consequential than the weather, then it doesn't touch their servers. It's not so much paranoia as it is threat mitigation. Google and Apple's services are incredibly useful, but if you depend on them too much, the loss of them could hurt, alot.
Like I said most of the other services don't have quite the reputation for uncalled for lockouts but here are a few news articles I came up with on a quick search:
https://www.androidpolice.com/2021/03/08/when-google-locks-you-out-of-your-account-begging-the-internet-for-help-is-your-first-and-last-resort/
https://www.nytimes.com/2022/08/21/technology/google-surveillance-toddler-photo.html (Paywalled)
https://www.theverge.com/2014/8/5/5970141/how-google-scans-your-gmail-for-child-porn
https://nypost.com/2022/08/22/google-bans-dad-for-sending-pics-of-toddlers-swollen-genitals-to-doctor/
https://news.bloomberglaw.com/privacy-and-data-security/google-flagged-child-porn-case-shows-court-split-on-privacy-30 (Paywalled)
https://bringmethenews.com/minnesota-news/innocent-family-photos-or-child-porn-investigators-face-tricky-case
https://www.npr.org/2021/08/06/1025402725/apple-iphone-for-child-sexual-abuse-privacy
https://english.elpais.com/science-tech/2022-09-19/google-closed-my-account-over-sexual-content-but-theyre-not-telling-me-what-it-is-and-ive-lost-everything.html
If your interested in learning more about self-hosting services out of you home you might check these out as a starting point:
https://github.com/awesome-selfhosted/awesome-selfhosted (Non-exhaustive list of services)
https://selfhosted.show/ (Podcast focused of self hosting services)
https://www.howtogeek.com/846979/heres-why-self-hosting-a-server-is-worth-the-effort/
- Yeah, I hear ya, but good luck getting your whole family, including elderly relatives, to use something you do control...
  It's a losing battle. You can share pics by a secure channel and they'll just repost it all over the place anyway.
  
  but good luck getting your whole family, including elderly relatives, to use something you do control...
  That’s one of the things I like about NextCloud. Even the most non-technical person knows how to follow a link in a email (to many an IT tech’s lament). All I do is share the file in NextCloud, maybe password protect it with a simple password, and copy the share link to the email or text message. Bob’s your uncle. Grandma Nosy-Britches gets to see the files but her email or messaging provider (Google, Mircrosoft, or whoever) does not…. At least until she shares the file directly. More likely though she will share the link. But that’s probably not something I’m too concerned about.
  You can share pics by a secure channel and they'll just repost it all over the place anyway.
  “A secret shared is no secret.” If you have a problem with something being shared, don’t share it. With anyone.
  I’m more concerned about accidentally tripping safety or security systems I don’t fully understand and having something I depend on suddenly cut off than I am the vagaries of dear Aunt Noisy. I can pretty well guess what Aunt Noisy or Grandma Nosy-Britches will do and it’s either not a problem or I’ve taken steps to avoid any problems.
  
  No pics for them then.
- great explaination

If you're wanting to be safe I wouldn't be using WhatsApp at all
- I'd add the caveat that a lot of the common options are even worse. There's at least encryption most of the time, in standard app operation.
  Via Element or Signal would be the best answer (or was last I checked), if there's was anybody else on there.
- you actually shouldnt use a phone, or internet either. /s

I feel out of the loop here. What's so secretive about a photo of a newborn?
- Some people just don't want pictures of their kids all on the internet. It could be seen as borderline paranoia by some people but I think everyone has the right to the level of privacy that they want.
  
  The best form of taking secure photos of your family is to take photos with a dedicated camera with it's own memory card. Develop the photo into a hard copy and keep the image digitally stored in your own systems and never share it online.
- Also CSAM detection algorithms are known to misfire on occasion (it's hard to impossible to tell apart a picture of a naked child sent for porn purposes and one not send for that) and people want to avoid any false allegations of that if at all possible.
- Also the world is a fucked up place
  
  😟
- Because the child might not want pictures of themselves on the internet. Its a right to privacy thing, at least here in the EU.
- Same.
- Yeah, babies are cute and all, but they all look the same for the first few weeks. If Everyone just had a standard library of like 20 or so pictures of newborn babies and everyone just picked one and shaired it instead of pictures of their kid no one would notice.
  
  🤭
  Is your name related to aphex twin?

What do you mean by safe?
- By safe I mean about privacy, if there's possibility that someone can "intercept" the photos of the child. Sorry if I didn't explain it well
  
  In computer security it always depends on your thread model. WhatsApp is supposed to be end-to-end-encrypted, so nobody can intercept your messages. However: Once someone flags a message as inappropriate, this gets circumvented and messages get forwarded to Meta. This is only supposed to happen if it's flagged. So unlikely in a family group. I trust this actually works the way Meta tells us, though I can't be sure because I haven't dissected the app and this may change in the future. And there is lawful intercept.
  Mind that people can download or screenshot messages and forward them or do whatever they like with the pictures.
  And another thing: If you have Sync enabled, Google Photos will sync pictures you take with their cloud servers and it'll end up there. ~~And Apple does the same with their iCloud.~~ As far as I know both platforms automatically scan pictures to help fight crime and child exploitation. We aren't allowed to know how those algorithms work in detail. I doubt a toddler in clothes or wrapped in a blanket will trigger the automatism. They claim a 'high level of accuracy'. But people generally advise not to take pictures of children without clothes with a smartphone. Bad incidents have already happened.
  Edit: Apple seems to have pushed for cloud scanning initially, but currently that doesn't happen any more. They have some on device filters as far as I understand.
  
  Interception by a third party is highly unlike, as the transport layer of basically everything is encrypted nowadays. What is left unknown is what can Meta do once the file is on their servers, as you'll have to trust Zuckk's word and Zuckk's encryption
  
  No , but they will get the meta data. But image should be secure. But then your recepient download it , upload it to Google cloud and so on
  
  If someone is able to intercept WhatsApp messages, they aren't using it to look at photos of your baby they're using it to spy on government officials
  
  you have to trust that Meta doesn't do anything with your pictures before they are sent and that the person you're sending them to doesn't backup their whatsapp stuff to google.
  It's more secure to use Signal

You could hand deliver them in a sealed envelope but it won't stop the recipient scanning them then sharing them on messenger, texts etc.
You'd need to consider where and how they get shared beyond the person you send them to, to then decide which level of privacy is appropriate. Ultimately, even though others don't recommend WhatsApp (nor would I) - it's maybe the best option in this case. Accessibility, ease of sharing just no guarantees on the encryption because the source is behind closed doors.

It depends on if you trust Meta. Generally speaking there is end-to-end encryption in WhatsApp, which means only you and the person you chat with can decrypt your messages / media (source). I believe there are some weak spots in group chats, mostly caused by users themselves. Not sure about the new Community function but I'd be careful with what I share there.
Some parties like Apple have decided to scan photos from your device for illegal material (edit: after backlash they dropped this for now, my bad). If using an app like WhatsApp I'd personally be aware that something like that might happen in the future as well. I'd not be surprised if some employees might (temporarily) be able to access more data than widely assumed, for debugging reasons in case of bugs.
Personally I take the risk for pragmatic reasons, but it doesn't hurt to be a bit cautious / aware.
- iirc Microsoft is doing it, read of a case where a parent sent a picture of his son to the doctor via onedrove share and his entire account got suspended over it.
- Some parties like Apple have decided to scan photos from your device for illegal material.
  No they haven’t, they aren’t, and they never even discussed scanning your messages like that. There’s a communication safety feature available to enable in parental controls so that if a child’s phone locally recognizes (using machine learning) that they received or are about to send a nude photo, the receiving photo is blurred and they’re given information about making safe choices and then allowed to continue or not.
  
  No they haven’t, they aren’t, and they never even discussed scanning your messages like that.
  They discussed it (source) but the backlash was enough to kill the project for now. Instead, they implemented the "opt-in" system you are talking about.
  
  Thanks for correcting me, you are right about the image scanning. Added an edit to my statement.

No. Never use a messenger for those things, that is legally allowed in most nations. They advertise e2e-encryption and stuff, but also need to comply to governments.
Remember e. G. The reason telegram's owner was kicked out of his own country because he didn't comply to leaving a backdoor for the gov? And how it's, in some nations, one of the only few messenger left that can be used to express a free opinion without "dissapearing" after?
With your pics you'll train AI-models for free at best.
I would never ever share personal stuff over some mega-corpo's "free" thing.
- but also need to comply to governments.
  I dont know about every country, but as far i know in germany at least you only need to disclose the information you actually have. Eg: if you dont have the encryption keys, the government cant do shit with the encrypted messages they habe
  So, correct me if im not right, but a messenger could be privacy respecting and legal at the same time
  
  Well, telegram e. G. Still is problematic in germany due to not complying. We in germany might be relatively safe for now, that's true. But don't forget what's at dawn for us. Then tgram & co will be banned and whatscrap will thrieve even more.
  I might come across as bitter, but that's only because i am 😁
- Agreed,. In a capitalistic economy, nothing is free.

Signal with a view once message is better than a lot of the available options. Also maybe threema, simplex or session but Signal is more popular nowadays.

Safe?
Yeah, safe in the sense that it would be difficult for someone to intercept and steal/alter. That doesn’t prevent whomever your sending it to saving it an insecure manner.
But there’s one REALLY important variable here/ nobody wants to steal a picture of your kid. Nobody cares.