How to test for an image fully inside another?

Calculate the offset of the first image over the second, and then check each pixel underneath the first image to see if the pixel below it is solid or not. If any pixels are over transparent pixels in image 2, or any pixels are over areas not overed by image 2 at all, then image 1 is not completely inside image 2.

; Calculate offset of Image 1 over Image 2:
Xoff = I2x - I1x
YOff = I2y - I1y

;Now, for each pixel in image 1, add that offset to its ;location to determine its location in image 2.

LockBuffer ImageBuffer(Image1)
LockBuffer ImageBuffer(Image2)

Inside = True

For Y = 0 to ImageHeight(Image1)-1
   For X = 0 to ImageWidth(Image1)-1

      ; Calculate the pixel in image 2 this pixel in image 1 is above:
      X2 = X + XOff
      Y2 = Y + YOff

      ; If the pixel lies within image 2:
      If (X2 >= 0) AND (X2 < ImageWidth(Image2)) AND (Y2 >= 0) AND (Y2 < ImageHeight(Image2))

         ; Is this pixel of image1 opaque?
         If ReadPixelFast(Image1, X, Y) <> 0

            ; Is this pixel of image2 transparent?
            If ReadPixelFast(Image2, X2, Y2) = 0

              ; Pixel1 is outside Image2.  Exit both loops!
                Inside = False
                Y = ImageHeight(Image1)
                X = InageWidth(Image1)

            else
               ; There are pixels from both images at this location, and both are opaque.
            endif
         else
            ; This pixel of image 1 is transparent, so it doesn't matter what is beneath it.
         endif

      Else
         ; Pixel is outside Image2.  Exit both loops!
         Inside = False
         Y = ImageHeight(Image1)
         X = InageWidth(Image1)
      Endif
   next
next

UnlockBuffer ImageBuffer(Image1)
UnlockBuffer ImageBuffer(Image2)