Why are file extensions case-sensitive on the web but not on localhost?

Question

So I was trying to link an image on my website as <img src="cat.png alt="cat"/> and for some reason it wasn't working. I later found out that when uploaded to my server the file was labeled as "cat.PNG" so I inputted that and it fixed. However, when I was testing my site on localhost, it was fine. Why is this? Is this some security issue or is localhost just smarter when it comes to parsing files?

I know this is a weird and random question but I am curious. Thanks.

Answer 1

That depends on the operating system. Your server seems to run Linux which is normally case sensitive and if you run Windows on localhost it's not.