The Elf archer on the right is out of the 4e PHB (not sure if it was
used before that or in anything else).
The way things like this work is a bit tricky and intricate, looking
at this logo I don't think it will be a HUGE issue because the images
themselves have been reasonably altered for the logo. There are
plenty of blogs out there that use Wizards images in their banners.
Worst case you'll get a cease and desist and you stop using the logo.
(at least to the best of my knowledge)
It was definitely the best logo that was submitted to the contest, and
my issue was that once I saw it I couldn't come up with anything
significantly better than it. Next contest it's probably best to keep
the entries private until the end to prevent situations like that. :D
-Danny