Any way picking points in texture space?

I have to pick a series of points on the 3D model using mouse, and translate them to texture space (uv coordinates). The position of points must be more precise than only denoted by vertices. Are there any ways doing this?

The points have 3 coordinates: x ,y and z. your mouse has 2 coordinates: x and y. So how do you want to find the z coordinate?
But maybe in special cases, you can use from a code to find the z coordinate(?)

You should ask that you want to pick some pixels from the window and use them as a texture.If it’s the case, you can use from the glReadPixels() and save the results in a file. then you can use from this file as a texture for your model.