Multiple Profile pictures in one profile indeed of explaining

I don’t have any problems with finding out how to add profile pictures to myself, however I had seen something from other people’s profiles  that I want to figure out how to do for my own profile. 

When you refresh the tab around someone’s profile or on a thread you may see their profile picture changes into a different image every time you refresh & It makes me wonder how they managed to do that.

I haven’t seen any threads or anyone mentioning how people do this to their profile but hopefully you guys may explain to me how it works & have a better understanding of how it works. :v 

I saved this website a while back, which is supposed to let you create the kind of alternating image thing you are talking about, though i've never tried it out personally ^^"

edit:

here is another thread I just saw where someone explains how to use the site I linked:

https://www.wolvden.com/chatter/topic/173606#299685

I’ll go test it out :v 

ived managed to figure out how to make my own pile however one of my images doent have a transparents background but instead is black & shrunk in size while the other one is pretty large in size compared to the first one.