Even if the uploader doesn't know what the green balls are, the caption could still simply say, "the green balls were not identified". Even that would have been a fair admission, and I would still have considered such a photo for POTD... there's nothing wrong with the educational discussion. But I agree caption-less photos should be disqualified as POTD candidates. One would hope we've moved wisely beyond just the shallow swimsuit competition... now we want our contestants to say something meaningful and intelligent too, and that's a good thing.

Instead why not write a caption yourself? (I often improve/enlarge the description and correct the English and formatting before I select a photo for POTD.)

I agree that some brief guidelines would be good. Jolyon?

EDIT: Saw that Frank had already compiled a list in

Thanks!