Upload & Sell: On
Don't think a contest organizer should (or could) be the arbiter of what is, or is not, a copyright violation.
Well, in this case, they have asked for "original work" as per this line from the contest rules: "Your submission must be 100% original work.” Further, Kevin Collins, in his Creative Commons license of the image, required that use of the image required attribution. In other words, the original creator of the photograph had to be credited with it's creation.
Leaving those considerations out, is the submitted image different enough from the original that it's has become an original work of it's own?