I'm a photographer with a Joomla web site and I would like to be able to have a viewer select an image from my gallery and then see it with a coloured frame and mat of their selection (a mat is the space between the frame and the actual image). I'm only looking to have a couple of different colour frames and mats. I have seen web sites that do this but I've not been able to find anything I can use with a Joomla site.

I do not think an extension exists. It should be done as a custom implementation.