This seems very handy – however the reference image would be infinitely easier to print on the correct size if it was a PDF file. PNG image format does not retain the resolution IIRC.
If you've worked with PNG files under Photoshop, you may have noticed that a picture saved with exactly 72 dpi has 72.009 dpi when you close it and open it again. Using an integer multiple of 254 for the dpi prevents such a drift.