Closing the results until the poll is complete assures a completely unbiased result, as much as can be unbiased within the scope of polls virtual environment. It prohibits undue campaigning on "election day" (election week?). It adds anticipation, and encourages participation.
After looking a bit - there is currently no way to add thumbnail images to the poll itself, only to the thread below it. I can see no reason for image redundancy, and there is some benefit from having folks go over to the submission thread and actually have a look at it, rather than just come to the poll, pick one, and vote.
Next month, names and possibly descriptions will be included with the poll.
Consider the thread beneath the poll as "exit survey" space, and you're free to submit additional images, or discussion. However, intentionally skewing the poll, such as posting a picture of guitar X, and calling it guitar Y in your post, would probably be cause for the post to be deleted, if not immediately corrected.