If you think you know what it is, and would like to take a guess, leave your answer(s) in the "share your thoughts (comments)" section at the end of this post.
I'm going to turn on the moderation setting for a few days so you won't see previous responses. I'll post any comments that are not guesses as I receive them, and all comments in a few days.
Have fun and good luck!
What do you think this close-up image is?