Hard way to hcange the size of a picture!

Hi everyone!
A long time since I didn’t post here.
My new problem is that I apply a texture on a grid(like in the lesson11 of Nehe Tutorial).
I use this gris to change the size of my picture ok?So sometimes it’s greater and smaller (yeah we know what change a size means!).
The thing is, the whole size change and I don’t want it!
I want that the bottom remains the same everytime, and change the size of the picture from this bottom. For exemple let’s imagine something like a cylender that can get out from the soil and grow more or less depending on the time ok? So for exemple hot time the cylender go out of the soil very high and cold time it just get out a little.
Let say that I got a picture of my cylender. The base of the picture represent the soil, and it never change. Now as I want to make my cylender grow more or less I got to find a way to enlarge my picture without changing the position of the bottom…I got no idea about how to do that…
Thanks to help me if you got any idea.

I think you can do that from changing the camera angle.

Keep the cylinder shaped normally, just adjust the camera perspective so that the top is smaller, and gets smaller as the object grows.