Changing the image with a transparent border over a static image

Hi there, so for my design assignment in my Web Development Class, I am required to use separate images to show the colours changing.

For example there is a static base image, (A Phone), the bezel however would be a dynamic image that changes to another image of a different colour. Effectively creating the illusion that the phone is changing it's bezel colour.

I'm not asking for you to do my assignment or the hard work for me, I'm more just asking for where I should start or even what I would search because I believe I am terribly under prepared for this assignment.

Epic visual tool

Epson 5030UB 2D/3D 1080p 3LCD Projector Submitted September 24, 2015 at 04:32PM by Frozen_Ships http://ift.tt/1KEcEJQ