The Design Studio we use is an amazing tool for customizing mat wear. Each piece of clip art you choose is vectorized, meaning that every individual facet can be manipulated. Both images and text can be altered, removed, or replaced as needed. Simply look at the bar to the right or click the part of the design you want to alter in order to work on it!
From there, the rest is simple. Upload your own art (it will not automatically be vectorized, so you may have to upload individual images or a vectorized file of your own) and attach it to anything you find!