Fake validation is less like coding as to catch a really well made fake you would need years of experience seeing all sorts of fakes , while coding needs only experience to see what is good code to able to catch most issues
If that were true, the software industry would have a much smaller problem re: bugs and errors than they currently do.
Sadly the problem is good enough is how the industry sees everything, constant cost cutting , off shoring or replacing senior talent with fresh graduates , inadequate focus on security, debt is all too common, unless/until something affects bottomline there is no pressure.
A fair point. I took "dollar bill" to be the generic "US currency" rather than specifically "the $1 bill". But this page covers everything from $1 to $100 (although it seems the $1 and $2 have barely any.)
USGOV has a pretty comprehensive guide on how to validate them:
https://www.uscurrency.gov/sites/default/files/downloadable-...