The problem I could foresee with this is that all/most writing prompts are just really irritating. A photo or something would be preferable.
Maybe I will allow users to submit their own prompts, or just have a randomized setting, character, and problem/goal.
Image prompts are an interesting idea, they never worked for me personally, but I'll think about adding them as an option.
Currently many prompts are taken from the top posts on /r/WritingPrompts, I'm an active user of that subreddit and I find them really helpful(they are usually specific and funny).
Do you have any advice on making a prompt good? Is there a kind of text prompts that you like?