In a competition campaign, allow user to check a checkbox (or something) to indicate that the random image generated will be either (1) images with no structured data, or (2) images which haven't been edited by other participants [during the campaign].

This is to make sure that in the campaign, the amount of work will be spread out to as many images as possible, and there will be an easy way to "fill the blanks" (images with no structured data)

I suppose the first method (finding images with no structured data) will be easier to implement rather than the second (finding images which haven't been "touched" by other participants)

After all images in the set have at least one structured data, then the algorithm could choose from the least amount to the most amount.

Also, does the randomizer generate an absolute random image, or is there some randomizer algorithm that you can share to us?