To get people to buy this sticker you need to:
1) find some photography groups and try to advertise your sticker there, example:
http://imvu.com/groups/group/photography%2BIs%2BLove/
Where you went wrong in the first place:
1) most people do not buy stickers
2) if there is a person in the sticker, people will not buy it unless either they are that person, that person is famous, that person is doing something extreamly funny, or that person is moving
Tip: either make something other than stickers, make custom stickers for a large group of people, or make a sticker that is entertaining