Does linux support images in .jpeg format? What is the difference if I save my image in
.jpg from a linux point of view? Is this case sensitive?
Linux supports jpeg format images. All three variants would be auto-magically recognized to be jpeg images by most modern linux desktop management systems and, for instance, be automagically opened by whatever default image viewing software your system uses.
As noted, linux file names are case sensitive - so it will consider files "foo.jpg" and "FOO.JPG" to be different files.
There are a lot of programs running on Linux that can handle JPEG files. It's up to them if they care about file name extension or not and how they do that.
So there are programs that will not recognise .JPEG but only .jpg as an file name extension for JPEG files, while others will even accept .mp3 or .doc as they just don't care about how you name your files.
Another point to consider: The whole .extension format is a windows thing, not a linux/unix thing. *nixs don't care what the file ends with, they read the file type from the header. So if you're having problems opening a .jpg file in Linux the problem is more likely with the file than with the OS.
Assuming you have Imagemagick installed (pretty common), you can just type
identify file.jpg from the command line and it will tell you what kind of file Linux thinks it's looking at. (It's should say something like:
file.jpg JPEG 80x108 80x108+0+0 PseudoClass 256c 19.5kb)