I believe that you have to make a render of them first, which means deleting all the background.
I have photoshop 9 cs2 and to do this i go to the eraser tool and right click it, so a new menu comes up
Then click background eraser tool.
Now click anywhere on the background and its should take away all of th colour, to leave cheques.
Now go back to the eraser tool, and select the normal eraser tool.
Now start rendering, just rub out all unwanted parts.
Think youve finished and got everything?
You're wrong, now go to blending ptions and go down to stroke, select this and press ok
Now you should have a red line all the way around your render. This is normal, this shows you how much unwanted parts are still left nxt to the image, if the red line is touching the image thn you done, and where it isnt give it a little bit of a rub out
Any loose red patches just rub out, because they are parts u must have missed that cannot be seen with the naked eye
Well thats my guide to rendering, hope it helps
it may have nothing to do with what u wanted, but its there for everyone else too