Why not open up your favorite photo editing program (paint.net is free and will do this), go to the magic wand tool (or use an eraser if you can't get paint.net) and select the pink, delete it. Unless your using MS Paint, it should be transparent when you save it. Why you'd use pink I don't know. If you don't have a magic wand here's how:
Use an eraser and delete all the pink. In SFML, you really can't do this without writing your own special and pointless line of code. However, I highly reccomend paint.net, because it makes doing this extremely easy.
The magic wand is a photo editing tool, google it.
Well if that is the case ok then. And thank you!
Already edit all my images. Did it with gimp...
Again thanks you very much on fast reply.