I think it's key to have a picture to work with and I think it might be helpful if the picture isn't too "busy"
I know there are guys like CI and Data who can really sink their teeth into isolating what they want and removing the rest, but I get kinda put off by all that extra effort.
I dunno, maybe that's just me..maybe I'm lazy. I'm willing to accept that judgment if it is thrust upon me. I just like a picture on a semi plain background so that I don't have to spend 5 hours cropping around the juniper bush so that I can get started on my actual creative idea.