You should automate the process of adding new puzzles, instead of manually adding them everytime.
Why not code up a queue (and put a set of puzzles in it) so that once someone has solved the picture, or the picture has expired, it automatically publishes the next puzzle for you?
Yeap I want to do that too actually.
Here's something different:

No hint this time! Could be item/person/title or even anything else.
Wow, no clue on this one. Maybe a screw or something? I could convince myself I see threads...
Btw, where are you pulling these images from? Your own personal collection or from around the web?