Graphics Quality & performance in Flash

Hi
I am trying to figure out the “Best Quality & Best Performance (easy to load )” Graphics

we All know VECTORS are considered best , but sometimes it makes too heavy

**Please check the link and tell what type of Images they are using , they remains good quality in even FullScreen **

https://www.zoombingo.co.uk/Other/PlayCasinoGame/tabid/89/Default.aspx?gid=41&practice=true

Please share best Ideas