Image captcha settings

The tab 'Images' on Administer » Site configuration » Captcha (admin/settings/mycaptcha/image) gives access to a few settings to influence image captcha generation.

Characters to appear in the image
Only characters in this textfield will be used in an image captcha. Those that can be easily mistaken for one-another in the font you are useing (eg i and l) can be removed.
Relative path to a TrueType font you wish to use. MyCaptcha comes with a number of Bitstream fonts in the font subfolder.
Minimum captcha length
The minimum amount of characters that appears in the captcha.
Maximum captcha length
The maximum amount of characters that appears in the captcha.

Next come a number of settings that add noise to the picture to make solving the captcha more difficult. As you can see in the examples below, those settings can be combined. Overdoing it might lead to a high percentage of captchas that aren't solvable by your visitors.

Be aware that some settings make it more time consuming, not impossible for a program to solve a CAPTCHA; most despeckle algorithms can clean up the dot noise, but they cost time.

CAPTCHA Settings
No additional noise
Double vision
Add dots as noise
Add lines as noise
Double vision, add dots as noise
Add dots as noise, add lines as noise