Place your tape on top of your image (here I'm picking circles from butcher paper (I have a massive roll that I use for palette paper, and this one had a painted paper drying on it), but you can pick up any image from a magazine, photo or your sketchbook. Burnish it thoroughly with your fingernail or a spoon.
If you're working on palette paper you can just lift the tape off and transfer to your background, burnishing it once again to secure.
If you're lifting something from a magazine or photo, merely cut around the image you want to secure, and use liquid gel medium to adhere it to your background.
If you wish to secure larger pieces (and goodness knows the paint spills on my plastic workshop tablecloths are endless), you can purchase cold laminating film from the stationers and use it in the same way.