Oliver Byrne's edition of Euclid is a nice proof-by-picture example:
https://www.math.ubc.ca/~cass/euclid/byrne.html
Altough, judging by the old timey language of the book, it's possible the book predates Hilbert's axiomatization of Euclidean geometry and the proofs in it were good enough for the standards of its time.
In modern mathematics proof by picture generally means you've drawn / pointed out a single example, possibly wrongly or in a way that doesn't generalize, and because you've shown that one example holds you assume all possible examples hold. That, obviously, needs not be the case.