No tourists on photo

[david]

An alternative method to achieve the same result is to use Hugin. This will even work for hand-held photographs, as Hugin can align photos to sub-pixel accuracy.
With the pictures aligned you can continue with Hugin, using "include" or "exclude" masks, or pull the images into GIMP and mask there, or use a median filter if it has enough information to work on.
david.