This is quite a good one, and not too difficult.
When 'wiping' in or out with Kdenlive, there is a considerable choice of standard wipe patterns, in .pgm or .png grayscale images.
You can choose from the list.
What if you want to expand the list?
Load any photo you like into Gimp, and convert it to a pgm.
Open a file manager as root, and add the new file to /usr/share/kde4/apps/kdenlive/lumas.
Then start or restart Kdenlive; your new wipe image will be in the list.
And the wipe system will use it.