Just try again. Make sure that the hashtag is at the 'Add up to 30 tags' box. I put the tag to that box and to the deviation description box and that worked. And I just used a random picture file that I deleted after I received the badge.
Any picture file works. Like any other previous badges this badge is given by a bot so it does not care if the picture follows the rules or not.
No. Any image works. I usually just upload a random picture file and delete it just after I receive the badge.
I just posted a random image file and then deleted it after I got the badge.