you can store pictures from OS var and recall it to use as a background.
To store pic from OS:
[Pic1]->Pointer

To use it on axe:
Copy(Pointer,L₆,768)

maybe I read the question wrong.
So far, you can only make 8x8 sprites.
to create a larger sprites, the only way to do is display multiple 8x8 sprites together.
If you're asking about making backgrounds out of sprites, you can always use the tilemap format.

What are you shooting for?  A pic the size of the entire screen or something like a 16*16 sprite?

For larger sprites the only way to do it afaict is to put 8*8 sprites together, and for screen-size pics you can use a TIOS pic or get the Hex (tho that's more complicated)

For sprites larger than 8x8, you can use Bitmap(). Unfortunately, it's much slower than 8x8 sprites.

You could also use the Copy() command to work with larger sprites.  I think I have an 80*20 sprites or so in Cube Droid in which I had a For() loop around a Copy().