I basically just cut out the various pieces and assembled them in Photoshop. A huge amount of color-correction and texturization was necessary to make things look okay.
The Painter in his Studio
Painted in 1650 by Dutch painter Hendrick Gerritsz Pot (1580-1657).
Currently displayed at Gemeentemuseum in The Hague.
Source: Web Gallery of Art
Mask used with the above.
Picture from Steve's web page;
it didn't need to be scissored because it already has an alpha channel.
The now-infamous picture of Zoran.
Mask used with the above.
Leonardo Da Vinci's Vetruvian Man.