Since TImagingBitmap is basically regular VCL TBitmap, you can use
methods described
here (scanline based one is better) or
here.
First check if width, height, and pixel formats match, then compare pixels if needed.
I'm planning image compare/diff functions for Imaging, but these will be for native Imaging image types (TImageData, TMultiImage, etc.), not TBitmaps.