There are a couple of ways to do it. The web developer could code the page to stack the images of the different uniforms on top of them, but hide all but the first image from view.

Then once a visitor moves their mouse over the first image of the uniform, the page quickly shows and hides each image. Creating the effect that the 'scrolling' effect you mentioned.

The developer could also stack the first image on top of an animated 'gif'. Once the visitor moves the cursor over the uniform, the top 'static' image hides, and the animated gif is shown and creates the 'scrolling' effect.

<--- Me when my head hits the pillow