The question is not the result of merge as far as I can see (there would be a note for that).
Getting multiple answers recommending the same or similar solutions happens regularly (there are other questions with the same issue). Sometimes it's just a timing issue (e.g. the two highly voted GIMP answers only have a four minutes gap), sometimes it's just the result of users not reading the other answers (or even competing for reputation). If you want to delete your own one, feel free to do that (personally I wouldn't bother with deleting it, it even got upvoted). There is a fourth one recommending GIMP which was deleted by the owner (that's why you can't see it) after realizing that others answered the same way already.
As for the answers with the commercial solutions: The asker didn't go into details about he is looking for free as "at no cost" or for free as "significantly cheaper than Photoshop", so they still are helpful. Don't upvote, maybe downvote even, but they are close enough to provide an answer that I wouldn't act on a "not an answer" flag.
In both cases it's a good example on how the voting system works on AD. Good answers (e.g. both the GIMP ones with their screenshots etc.) get voted up, bad answers (or those somehow missing the point) get down voted or at least not up voted so much. I see no need for any additional moderation activity here.