Overall well done captcha generator, however it still could be improved.
First I missed some options, at least to define the letter spacing of the captcha. I tried different TTF fonts, all with a minimum size to be readable, but often the letters were placed outside of the image. It had to be enlarged to extreme sizes.
I think there is also need for some more distortion possibilities (e.g. to randomize particles or a setting to overlap letters, generally randomization is implemented very rarely).
Installation of another Perl module (GD::SecurityImage::AC) was required for me, because the Security-Image module comes without any captcha handler. Usually you are supposed to create that code yourself - which should be no problem if you are an experienced Perl programmer - but I am certainly not.
Besides those glitches there were no problems, installation was easy, there is a very good documentation available and I experienced fast and helpful support by the author. GD-SecurityImage worked perfectly together with the above mentioned AC module.
Love this tool. Simple interface. Well documented. Easy to install. Works with both GD and ImageMagick. The name is misleading, which makes it difficult to find for those who know what they are looking for. Must be renamed to Image::CAPTCHA, or Image::Captcha instead.