I realize that your stated use case is photos used in HDR where there may be minor differences in alignment but the scale is the same. I wanted to use your tool when an original photo has been copied, cropped, then rescaled. The primary subject matter of the photo (say a human model) is retained in the copy but often the original visible watermark has been replaced with the pirate site's watermark. In testing your module, it was unable to come close to the original image in terms of rescaling the edited photo nor matching the cropped, rescaled photo within the larger original. I am opening the original and edited photo as layers. I select the edited photo as the current layer (Gimp 2.6.11 on Ubuntu 11.04) then select the original layer as the registration object in the drop down. I set the iterations to max. Am I missing something obvious in how your module functions or does it not work in these circumstances? If so, can it be modified to handle this as it would be very useful.