Can an attacker on the network see plain HTTP requests?
Yes, they can. They can also modify the request as they want.
Can an attacker on the network see HTTPS requests?
Depends. If the attacker is the one using your app, then they can. If the attacker is trying to spy on others, it becomes more difficult, but it is not impossible.
The one thing you have to be careful with is placing too many restrictions on the person taking the photo.
What if the person wants to use their own camera (not a phone)?
What if the person has a disability that makes it difficult to take clear pictures? My hands shake and if I was hired to take pictures, I'd bring my kid or a friend with me to actually ...
Here is a list of tips/techniques that you can use:
If users are authenticated and you assign a unique uuid, just allow one TCP/HTTP/HTTPS connection for a given uuid. By doing this, you will limit the number of connections to your service that can use the uuid.
If somebody wants to reuse a uuid or do a "uuid attack" by flooding from requests you can use a ...