To make raised textures on Polymer Clay artists use specially made sheets or stamps which they press into the clay. You can make your own by pressing textured things into flat pieces of raw clay, baking it and then using that baked clay as a texture stamp. People use leaves, tree bark, in fact just about anything with an interesting texture on it. I've had some fun making these myself.
It is achieved by using something called Photopolymer Gel, which is a kind of rubber/silicon which is sensitive to UV light. You shine the UV light through a negative image, and the black part goes hard and the clear part stays liquid (or possibly the other way round. . . ) and can be washed away leaving a rubber stamp. The negative image might be a print on acetate of your computer image. . .
So, this is what I did. Sparing you further explanations, here are a couple of examples of the images I used as negatives.
And here are a couple of examples of textured items made with the texture sheets derived from those images and other similar ones. . .