Would this work to make the voting more accountable?

Any vote between 2 and 4 could be submitted without comment.  These are votes which indicate a neutral feeling towards the image, so no real comment is necessary.  The votes also don't really have a huge effect on the final ranking of the image (or at least not as big as a .5 or a 5 would).

Any vote cast with .5, 1, 1.5 stars would open a "comment" field.  If the voter didn't type anything in it, the comment would be blank, but the ID of the voter would still be listed.

Any vote cast with 4, 4.5, or 5 stars would also open a comment field.  If the voter doesn't type anything in the field, the comment would be blank, but the ID of the voter would still be listed.

At the end of the challenge, each of the entries would have their final vote tallies, plus a column of "negative comments" and a column of "positive comments".  Each of the comments, and the ID's of the associated voters (and if they didn't leave an explanatory comment, then just their ID) would also be shown in the appropriate column.

The above would result in much more feedback for every image (that got votes that were either above 3.5 or below 2), which would be a good thing.  It would also show which voters are sandbagging/voting down the other images to try to boost their own result and which were voting up their "family members" or "other friend who attended the same photo shoot".

The above would discourage people from voting... so to counter that then the rule would have to be that you earned the right to enter a challenge for every 50 votes you cast.  The votes would not have to be in your challenge, but you would have to select a challenge that interested you and cast the votes in order to build up your vote count so you could "trade them in" for a challenge entry.  With that system, on average every image would receive 50 votes (or more, because some people might choose to vote more than 50 times for every entry they make) and the effect of those voting it down would be reduced.

And a thought on voting in challenges in which I've entered...

At first when I entered challenges, I would vote in all of the images of the challenge (except my own).  I then realized that I was voting against my own images, because I was giving 4 or 4.5 or 5 star votes to the images that I thought were the best... and looking over the challenge results usually the winning image has a composite score of around 3... or at most something less than 4... so even if my image was getting a composite score of 3.5, my vote cast for a competing "good" (in my opinion) image was giving raising that image's score to higher than whatever the winning score would be... and since I wasn't casting a vote for myself, even if my image was the winner I'd effectively be raising the score of all of the main competition while not affecting mine.  Once I realized that, I decided to stop voting in challenges which I had entered.  Instead, I vote for every image in a different challenge that has subject matter which interests me.