HUGE Dragonshard mini_image compressed to 634KB

[whoeverxxx]

I downloaded the Dragonshard mini_image at GCW and noticed it was over 1 GB in size, compressed to 634KB with Winrar. I made a much smaller working mini-image for the game but I have no idea how that huge file was compressed like that using Winrar. I'm using version 3.20 of Winrar and when I compress files they are not much smaller than the original. I'll admit I don't compress files much but this makes me wonder if the newer version of Winrar lets you compress files to that extent or if I'm missing something on my version or I just don't know how to use the program enough on the packaging end. Can someone shed some light on the subject?