Many Items in the textsanitizer are configurable via php config files.
These should be moved to a new preference category eg Display options.
There can then be set if the Carica routine is to be used, and the width for limiting the images.
Other preferences in this category allow the setting of the captcha parameters etc.
This would allow personal settings and variations in the captcha images, what makes it also more difficult for SPAMmers to crack it.
In general all file configurations should move to the preference system.