This has been absolutely baffling me. I scanned an image both vertically and horizontally on the flatbed of my HP Color LaserJet Pro MFP M277dw using Windows Fax and Scan. I then used Gimp to rotate one of the images 90 degrees, to overlay it above the other image. But then, the image appears to have been stretched by the flatbed!
Not giving up, I tried on another scanner, the Epson Stylus C88+, and got the same results! Is there an inherent flaw with most flatbed scanners? Why does it seem to skew out the image when compared to its horizontal counterpart?
In the 3rd image below, if I lined up the "A", the "D" gets misaligned. The graphing paper also shows the effects of a horizontal scan.
Why does this happen? Are there any scanners that don't do this? Is it dependent on the angle that light is reaching the photo-sensors?
Finally, can this multi-angle scanner invention have anything at all to do with this effect?