Well here´s the thing, I am using the Terminal to do this. With a text editor such as nano I create a plain text file with the content: "GIF89a2017" and I save it as rare.gif
Here´s the thing, when I do file rare.gif it gives me this output: rare.gif: GIF image data, version 89a, 12338 x 14129 and that is indicating that it is a GIF image with a resolution of 12338 x 14129 and that's what I don't understand. Where´s that resolution coming from?
Another thing is, I thought extension didn't really decide what type of file it is, for example when I take a .gif and convert it into and .exe it still recognises it as a GIF image with the file command. I'm gonna guess that in the problem that I have it is recognised as a GIF image because it was created with the GIF extension but I'd like to know why.
Thanks to everyone!
Where´s that resolution coming from?
It's coming from the (bogus) GIF89 header you put in the file. The four bytes following "GIF89a" define the width and height. Each one is stored as a 16-bit unsigned integer. The characters you put there -- 2017 -- are interpreted as:
32 30 ("20") -- 0x3032 = 12338
31 37 ("17") -- 0x3731 = 14129
I'm gonna guess that in the problem that I have it is recognised as a GIF image because it was created with the GIF extension but I'd like to know why.
No, file doesn't look at extensions. It's because the file had a semi-valid GIF header. If you changed the header to something that didn't start with "GIF89a", it will no longer be recognized as a GIF.