[Answer]-Best way to check if picture already seen

I don’t know much about Django, but either you need to do as you suggested, or you can ask for a random picture, the server responds with the ID it intends to send and your app replies with either yes or no depending on whether it wants that one. The server then either offers another random ID or you accept the picture and it sends it.

Also, use a set instead of an array – you have no interest in order, you just want to avoid duplicates.