Can we add a borderless image in a theme with default image borders?

I have run up against this problem twice. I designed my site themes in Artisteer 2. By default, images receive a predefined border. However, sometimes you just want to add an image without a border.

For example, the WordPress logo:

http://thepaintedgarden.x11s.org/WP/one-column-themes/

And my own logo (the Lion):

http://dreamthemes.x11s.org/WP/christmas_tales/

I am not big on css and editing installed templates. Does anyone know of a way to add code locally around the specific image to keep the border off it?

Thanks in advance.