I'd think this is not a good idea. You're essentially trying to break a stenographic code yourself. If you find nothing, was it not there or did you just not look hard enough?

If it matters if it's there or not, assume it's there. It's really the only safe option.

To answer the actual question though: how I'd start would be, scan a blank piece of paper. Print something small on it. Scan it again. Look for any differences using digital imaging tools. This should allow you to potentially find invisible differences.

You can also try to tell while it's printing if it does something to parts of the page that you didn't print to. Print at the bottom of the page only. Do the print heads engage anywhere else? Do the same thing with the middle.

This describes the process of finding the dots: https://blog.erratasec.com/2017/06/how-intercept-outed-reali...

There is an advantage if you are testing printers rather than reviewing a single scan as they describe - you can print the same content on two different printers and compare the output