Some times you need to block visitor access to specific file types that is not being used in web server.You can make that possible by using .htaccess.Look at the example given below. First of all open .htaccess file in public_html folder(if it is not there just create one). Add the below lines to it.

<Files ~ "\.jpg$">
Order allow,deny
Deny from all
</Files>

The above .htaccess will block the files with extension .jpg . If you want to block multiple file extensions seperate them as follows.

<Files ~ "\.(jpg|inc|3gp|sh)$">
Order allow,deny
Deny from all
</Files>