If you want to change image background on image with wrong proportions:
This can be changed in strict_image.php
This vars:
public $back_red = 197;
public $back_green = 197;
public $back_blue = 197;
After that you should remove all cached files inside folder: files\strict_cache
Hints:
Color detection: http://iwinter.com.hr/support/?p=9061
Another solution, file strict_image.php: