The Canon Selphy CP1300 dye-sublimation printer offers borderless edge-to-edge printing on 100x148mm media ("Postcard" size, in Canon's language).
Unfortunately whether printing from a computer (macOS in my case) or from an SD card attached directly to the printer, what is actually printed is always cropped, on all four edges, by a few mm.
This is even the case when the image is in precisely the same 100x148 proportions as the media.
For most photos losing a few mm doesn't matter, but for images that have already been carefully cropped it does.
The image below shows how a particular image appears in the print preview, both in macOS and on the printer's own display when printing directly from an SD card; the yellow border approximately contains the area that is actually printed.
None of the settings applied either in the printer driver or on the printer itself call for images to be cropped in this way.
It seems pretty clear that this behaviour is in the print engine itself, though I can't think what purpose it serves. Is there any way to override it? The printer has a configuration web page and I was hoping I might find some low-level settings (no luck).
It's mostly just annoying, and for the occasional photo where it's really crucial to get all the edges in, I could add a border so that the cropping removes the border rather than the image - but that's not a very satisfactory solution.