You can draw a little piece of big texture to little texture. Then you can use that little texture as you want.
Code from the video:
--preparations
local cbst = LoadTexture("abstract::cobblestones.dds")
local buf = CreateBuffer(128, 128, BUFFER_COLOR)
local tex = CreateTexture(128, 128, TEXTURE_RGB)
SetColorBuffer(buf, tex, 0, 0)
--render image to custom buffer
SetBuffer(buf)
DrawImage(cbst, MouseX() - 512, -(MouseY() - 512), 1024, -1024)
SetBuffer(BackBuffer())
--draw custom buffer to back buffer
DrawImage(tex, 100, 100, 128, 128)