So basically I would just have to screenshot the image or export it to a new file type that doesn't support their fancy encryption and then I can do whatever I want with the photo?
The point is that they can show anybody interested the original with the signature from the camera.
The problem is that you can likely attack the camera's security chip to sign any photo, as internally the photo would come from the cmos without any signing and the camera would sign it before writing it to storage.
It's signed, not encrypted. Think of it as a chain of custody mark. The original photo was signed by person X, and then edited by news source Y. The validity of that chain can be verified, and the reliability judged based on that.
Effectively it ties the veracity and accuracy of the photo to a few given parties. E.g. a photo from a known good war photographer, edited under the "New Your Times" newspaper's licence would carry a lot more weight than a random unsigned photo found online, or one published by a random online rag print.