Fastest way to tell if 2 surfaces hv same image in DirectX

i gues by *image* you mean the texture? can you explain a bit more and what you are trying to do?

Even pixel by pixel comparison requires an analysis. For example, the texture (I understand that ikework guess is correct) can be applied in different ways, say different angles or scale or repeating times) and the texture are different, despite the source images to be the same.

You should take on count how are assigned the texture coordinates, how they are combined/interpolated, if it is subject to level of detail (mipmapping)... a lot of modifiers to the image... how about lightning (luminance is affected by)?

Depending on your code, you can look for the load texture file, or for named textures...

Anyway, after mapped and transformed in screen coordinates, the individual texels of a texture rarely correspond to individual pixels of the final screen image, so I understand that you want compare actual images in the 3d space, not when projected in the screen.

Concluding, it is mandatory to define the comparison criteria, which modifiers are considered or not.

To be simple, the easy way is to superpose the two rectangles to be compared and subtract their textures (GL_COMBINE_RGB and GL_SUBTRACT), expecting zero texels values if the images match...

Jose