As it was, I didn’t need to avail myself of the services of the GIMP as all I needed was on my iPad.
So, the window assembled:
It’s 45mm by 100mm
After editing for size etc, the image was horizontally flipped so that St. George could be read from inside the church. The basic window was already assembled with the laser cut frame superglued to vacformed blister styrene (the vacforming leaves nice distortions in the glass). The printed face of the acetate was then covered in superglue and the window stuck to it, sandwiching the ink in the middle.
I expect I’ll trim and fit it tomorrow.