You could use rot13 as an extremely simple encryption.  If you want it more secure, just make some other mapping in memory and do a lookup.  For instance:

{Data('D','A','B','C')+A-'A'}
For input character A, it maps 'A'->'D', 'B'->'A', 'C'->'B', 'D'->'C'

After storing some values in Pointer, is there a way to "DelVar" it?
Every time I run the program, the Pointer still have all the values.

You can't predict whether modifications to static variables will be saved (since these "variables" are really part of the program's data itself, it all depends on whether or not the user's shell writes back programs or not). Instead, copy the initialized data to a safe RAM area like L1 and work with it there, so you never have to modify the program itself.

what I do is store Pic1 to pointer and do this: Copy(Pointer,L6,768)

Try Copy(B,L3,768) instead of Copy(B,L6,768)r which actually copies backwards instead of forwards and probably corrupts stuff

What was L3 again?

The backbuffer

there's also the really handy DispGraph(ptr),DispGraph(ptr1,ptr2)^rr