Pinto patterns are one of those things you just have to learn to spot. My advice is to learn tobiano, and just know everything else is overo. Tobiano is easiest to learn, example
Common characteristics, see the spot on her chest? The spots on her flanks? And you can't see it, but a two toned tail (white on top, color on bottom) are tobiano traits, also solid heads (stars, strips, blazes, are all fine, but no bold or apron faces, and blue eyes are overo traits). She's pretty traditionally marked, so I'll show an example of one that is minimally marked,
This one would be harder to learn to spot becaue she's so minimally marked, but the white feet, higher in back, and the spot on her butt that crosses to the other side are good indicators, and I've seen some w/ just a diamond of white over the withers.
Some examples of overos,
Both these are minimally marked, but thier faces give them away,
Need a better pic of this one, he's abit louder then the other two,
And then here is a tovero,
I consider this guy a medicine hat, but not really sure he qualifies w/ one ear not being completely white. To be a medicine hat they just need a 'hat' of color over the ears, the body can be any color as long as the head is white and ears are colored.
And just a note because I expect to get flack over it, I know they are now saying ANY white markings are some form of pinto, blazes, stars, snips, socks, etc., but as far as I'm concerned those are just normal markings and a tobiano can have them, I don't consider solid horses pinto because of these markings either. I love all the colors and patterns, but I think that's complicating things abit to much!