You can do it in many softwares like photoshop, illustrator, corel draw... I use Photoshop anyway. It's hard to explain the whole thing so I think you can search "vexel tutorial" here, surely there're lots of amazing stuff show you how ^^
I love it! It's beautifully done, but if there's one thing I change is how close she is to that window frame. She looks close enough to the edge of that frame to create the impression of a tangent and I'd move here a further away or a bit more infront of it. That would be the only thing though.
Thanks for pointing it out. You're completely right, I took this one. That's my problem I think, I'm always lazy and lack of idea when I'm about to finish the main object and don't know what to do with the background =.=