readpixel, and writepixel, lets you read and write pixels from a screen
readpixelfast and writepixelfast, are the faster ones, but have no error checking, and need you to lock the screen buffer.
You can use createimage
if you create one, set it as the current buffer
draw what you want to it.
then you can paste it with drawimage.
It has been years since I have touched blitz3d, wrote an openGL engine in it, then ran away hehe.
I had so much fun with blitz+, and blitzMAX.