I can't really tell, but this looks like part of the window frame is pulling away from the wood frame to the house. In other words, the window itself has this sort of vinyl piece that I guess is supposed to mate up to the house, and it seems like it is pulling away. I have a few doing this. Hopefully this picture will help:
Is this common? Should I just tack it in with some small nails or some "liquid nails" or other glue like sealant?