TOPIC: Button not "really" showing up

The IMAGE button are not always showing up on certain old computers... I work in a school...

So, is there a way to change the defaut IMAGE button for that ugly standard one, to make it sure it is fully compatible in all environnement? This problem seems to be only on the registration form ("Next step" button... sorry, I use the french package... I don't know what it is exactly in english).

The button does not show up by itself, but, if I move the mouse over, it WILL appear (?)

Thanks again.