Many times in my career I’ve received a logo from a customer as a JPEG image with such bad artifacts that it was unusable in a website. Sometimes I’d manage to get it in a different format after a request but sometimes I was told that this is all they have and thus had to retouch it while dreaming of receiving it as a vector image to begin with. While receiving an image in a wrong format from a customer is not that bad (after all, they are not those who publish it), I often encounter wrong format when browsing the vast space of Internet and the people who published it should have known better that the chosen format is wrong. Moreover, I’ve even seen graphic designers to choose JPEG when PNG would be a better option.
Thinking why people get it wrong so often I tried to come up with a flowchart for selecting the right format out of the JPEG/PNG/GIF trinity, thus omitting other (possibly more suitable) formats like SVG.