These ones are my first "secret door" image, printed on self-adhesive label paper, and stuck to 12mm MDF. I might possibly go to 18mm for added stability, but I'll see how these go in play first.
The black edges are problematic. They'd be better covered with the stone pattern, but the edges of MDF aren't an ideal surface for sticking the label paper to unless it's sealed and sanded pretty smooth, which means more trouble than I really want to go to. Maybe as a partial fix I'll paint the sides of the blocks, where they're more likely to be exposed, in a roughly stone-like colour — it would still be a bit of a dislocation, but they wouldn't stand out quite as much when they're butted up against each other like this.
What I want to end up with is something like the Fat Dragon card dungeon bits, but with more weight and stability.
I've saved it at 300dpi, but I don't know if Blogger's image uploader will preserve image resolution information. The physical dimensions of the image are 50 x 50 mm, so if it prints bigger than that, then you'll have to find some way to adjust it (such as embedding it in a word processor document, resized to the right dimensions.... though that sort of kludge makes me sad).
Later...I later realised that I had a roll of 12mm double-sided tape, and since the MDF is fortuitously also 12mm, I could make my own block-pattern edge banding tape with relatively little travail.
Which I have now done.
As I suspected, it is a great improvement.
I tried out a single wrap-around image for a standard dungeon door, but I found that it made the location of the door sides centrally on the block on both sides difficult — impossible, in fact, without getting a lot more pernicketty about my measurements.
So instead I went back to separate individual images for each side, but this time with sufficient overhang to wrap around and cover about 60% of the width of the block. There is therefore a line up the sides where the two images don't tile seamlessly, but it's not at all noticeable unless you look for it, so I call that a win.