Many of my templates include customized featured gallery icons. The locations of these icons will vary depending on the template, but the technique for creating them is always the same. These icons will have clipping masks that you can use to insert your own images. Sometimes they will also include text that you can modify.
The video explains the process of using clipping masks to prepare your gallery icons and how to replace those icons in your site. The location of the gallery icons in your template will be supplied in the template PSD.
View the video: Gallery Icons
Here are some examples of how gallery icons are used in some of my templates: