So I have an image thumbnail, 100x150 let's say. And I want to draw a box on that thumbs to represent a 8x10 image. So 100x150 would be a 8x12, I want to draw a box that is roughly 100x130ish centered. This would give people a representation of what an 8x10 print would look like as it's much smaller than the 8x12 original image.
Here is an example of what I mean.
So the thumbnail would look like this:

And when they select to purchase an 8x10, it would look like:

Now ignore how the box looks, it can be a simple line, we don't need to be fancy, the idea here is to prompt the user ordering the 8x10 to choose how they want it cropped... and if this doesn't work for them, they can purchase another size.
Any help would be greatly appreciated!