This question already has an answer here:
Say I have a trapezoidal prism (a six-sided object with 4 trapezoidal faces and a rectangular top and bottom) like this one here.
I need to apply a displacement modifier to one trapezoidal face using an image containing the texture/normals, such as this crude example.
In other words, I need to take an image that is the same shape as the face and use it to create the actual 3D texture using a displacement modifier (the resulting object will be 3D printed).
I know how to do this on a simple plane/surface, but I'm running into trouble in this scenario. The main problems seem to be:
How do I apply the displacement modifier to only one selected face, without affecting the rest of the object, and
When I apply the image, how do I force the image to fit correctly onto the surface, as they have the same proportions but may not be the same size?
Edit: This has been flagged as a possible duplicate of this question. I did see that question before posting mine, but it did not help me. It does not cover how to apply displacement modifiers to only one face without altering the object, and does not touch upon the second part of my question at all.