Not enough Key points to stitch

I downloaded three scans from a pinball playfield to stitch into a single photo. Program repeatedly tells me I don’t have enough key points to stitch. This is nuts. The graphic is full of very specific images and should have plenty of detail to stitch. I tired three long scans the length of the playfield and then 5 short scans across the width of the play field. All in color all in high resolution 1200 DPI. No luck. $20 wasted.

wh571 about PhotoStitcher, v1.6