How change the captcha noise images
Change the images
Modx offers by default 4 noise images.
In order to change them to match your website you have to navigate to manager/includes/noises and replace those 4 .jpg files with new ones.
The new noise images will be used by the manager login page, Jot and probably eForm. Other snippets might make use of them as well.
Add more images
To add more images you can modify manager/includes/veriword.php file.
Just change the following line to match the number of images you want to use.
/* pick one background image randomly from image directory */ $img_file = $this->dir_noise."noise".rand(1,4).".jpg";
Change "4" to your total number of images.
Note: When upgrading the noise images and veriword.php are replaced. Make sure you you keep a copy of your images and modify the verioword.php accordingly.