Don't know how OGL manages VRAM but it *will* load every drawn image from RAM to VRAM and, afaik, you cannot remove it. I have only checked the source for DX which will remove or replace unused surfaces when a threshold is reached on the 'last-used/least-used' basis.
<EDIT> What I am trying to say is that you can decide when to move them from RAM to VRAM (by drawing them) but cannot decide when to get them out of VRAM.
<EDIT> What I am trying to say is that you can decide when to move them from RAM to VRAM (by drawing them) but cannot decide when to get them out of VRAM.