This sounds like a fun project! Told2be has a good idea -- if you can do this yourself, you could find an image you like, put gridlines on it, then try transferring a scaled image onto the wall using a bigger grid guidelines -- maybe practice the technique on large papers first. Another often used technique is to project the image onto the wall and trace....
Finding talented student(s) that might do the job for you is great suggestion, too. Maybe the teacher could tie it into their curriculum work (spring semester project, etc.).
If you can add three dimensionality, tile/mosaic accents -- within the image, frame border, or even just a baseline -- might be fun, too. I think there must be sources to get free or dirt cheap excess/remaining tiles.
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