How was treehouse website course boxes developed using images?

I am looking at the treehouse website I see that the course boxes were developed using images, if so, how was that done. If not, how was it done? look at references here:

https://d9hhrg4mnvzow.cloudfront.net/join.teamtreehouse.com/techdegree/21b4a261-fewd-v2.png https://join.teamtreehouse.com/techdegree/

If this is just the way it is disabled for users without a subscription than how does the actual website display these course boxes and inside the course page?