Hello,

I tried with this but it did not work even if I cleaned cache:

#footer #osticket,
#footer #ostawesome {
    display: none;
}

Something else I should do?

Okay guys, make sure you add this code to /osta/user-styles.css exactly as below and you will no longer have images in the footer in desktop or mobile orientation:

#footer #osticket a,
#footer #ostawesome a {
    display: none !important;
}

If you don't see the changes right away, be sure to clear your browser cache.

This works. In fact, your first code worked as well.  I forgot to clear cache on my mobile browser. 

Super!