change buttons for my own images

You'd need to override our CSS files to do that. For information on how to update the CSS and create your own theme, please see our Joomla login themes documentation.

I hope that helps,
Alex

That option you point to is only for setting specific images for the social login icons, which are only available if you're using JFBConnect.

As mentioned in the Themes documentation, "To create a template override, you'll first need to create the following directory:". Those directories won't exist in your template's folder until you create them.

Once the directory is created, copy the theme CSS file over from the /media/sourcecoast/themes/sclogin/ directory that you are using. Then, the main styles you want to target are:
Main login button:
.sourcecoast .btn-primary
Register button:
.sourcecoast .btn

With those, you should be able to override or set any settings you want for those HTML elements.

I hope that helps,
Alex

Glad to be of help. If you need anything else, just let us know.

Thanks,
Alex