Did a little web surfing and found this tutorial: http://www.photoshoplab.com/ripped-and-torn-edges-and-stuff.html
It was written for a previous version of Photoshop so I had to ignore the F5 command to open the brush palette. (By the way, have you ever played with the settings in this palette? They'll really open a world of control possibilities for brushes)
After going through the tutorial I saved the adjusted brush as a brush preset and opened up the original of this image. I put a white border around it and just using the preset I had just saved and white paint brushed around the edge of the flower picture. The results lacked the transparency that I wanted so I just brushed again to make the edge whiter.