I don't use the same clients for viewing and editing.
I mostly use OSMAnd for viewing (but it can do editing too). To edit I use StreetComplete for easy, gamified, contribution and Vespucci if I need a full on editor. StreetComplete only ask you missing information about the things around you, if I want to add something new I use Vespucci).
website:menu=* – url to menu of the restaurant (pdf or webpage)
So there's no way to just upload a photo of the menu when you visit. And if a restaurant doesn't have a website with a menu, there's no way to add a menu.
Basically no, you can't upload pictures. Even if you could add menu prices (I didn't check) it's not easy enough for enough people to bother, and will easily go out of date quickly. If it was as simple as uploading a photo it would be viable.