Many (most?) programs note file extensions in lower case.
ls command in bash even prints
foo.jpg highlighted as picture by default but not
Lower case characters are better to distinguish from each other because they make use of descenders.
Is there a standard or convention that suggests to prefer lower case file extensions on Linux systems?
(similar, but different question: https://softwareengineering.stackexchange.com/questions/186313/lowercase-in-linux-file-names)