Clipping Masks are pretty powerful when used with shapes or type. Essentially, it allows the type or text to serve as a mask, permitting the images to appear only within the type or created shape.
tFor this to work well, I recommend using a thick typeface (I’m using the type “Phosphate Solid” for the example above) to make it easier to see the images that will reside inside. After typing some text in, bring in your images as separate layers into the file you are working on. It’s important to stack your images ABOVE the type layer for this technique to work.
Right click (control click) to the right of each image layer within the Layers panel and select Create Clipping Mask. Voila!
Clipping Masks should be part of every designer’s skill set. Give it a try!