For writing text on images, did you mean the banner at the top of the site? If so, that doesn't use GD, it can be found in your theme's template.tpl file towards the top, similar to this:
HTML Code:
<div id="wrapper" style="text-align:center;">
<div id="header"><a href="{$path}index">{$site_name}</a></div>
Just replace {$site_name} with something shorter if the name it's pulling is too long.
If not, what were you referring to? Since I haven't noticed any other instances where mysidia does this.