The BMP RLE decoder's delta escape handler reads the displacement bytes twice from the file stream. It reads 2 bytes intobytes_read for validation, then callsself.fd.read(2) again instead of unpackingbytes_read:

bytes_read=self.fd.read(2)# read delta bytesiflen(bytes_read)<2:breakright,up=self.fd.read(2)# reads 2 MORE bytes, discards the actual delta values

The real delta displacement values are thrown away, andright /up come from whatever happens to be next in the stream. Any RLE-compressed BMP that uses delta escape codes gets decoded with wrong pixel offsets, producing corrupted output.