[cesarb]

> image viewers do not trust the file extension and ignore it

Not all of them; for instance, if I rename a .jpg to a .png exension and try to open it with Gnome's EOG, it presents an error saying "Not a PNG file", instead of showing the image.

[WillDaSilva]

A behaviour which I'm quite fond of, as it allows me to fix the file extensions. I generally don't like relying on the file extension for information, but it helps me keep my media collection clean in this case. It'd be ideal if it displayed the image anyway, while also displaying a warning message that says the extension doesn't match the actual file type.