To complete @GauravKachhadiya's answer :
means "hide only .jpg extension files from indexing.
IndexIgnore directive uses wildcard expression to match against directories and files.
a star character , it matches any charactes in a string ,eg : foo or foo.extension, in the following example, we are going to turn off the directory listing, no files or dirs will appear in the index :
Or if you want to hide spacific files , in the directory listing, then we can use
*.php => matches a string that starts with any char and ends with .php
The example above hides all files that end with .php