# ecaptcha **Repository Path**: summergaolib/ecaptcha ## Basic Information - **Project Name**: ecaptcha - **Description**: Zero-dependency Erlang library that generates captcha images - **Primary Language**: Erlang - **License**: Apache-2.0 - **Default Branch**: master - **Homepage**: None - **GVP Project**: No ## Statistics - **Stars**: 0 - **Forks**: 0 - **Created**: 2021-08-09 - **Last Updated**: 2021-08-09 ## Categories & Tags **Categories**: Uncategorized **Tags**: None ## README ecaptcha ===== Simple [Captcha](https://en.wikipedia.org/wiki/CAPTCHA) image generator for Erlang. Zero dependencies! Pixels are generated by tiny C NIF. GIF and PNG encoders are pure-Erlang. Flexible additional effects, multiple fonts, arbitrary colors, latin alphanumerics set of characters. Covered by property-based tests. No segfaults, no memory-leaks. Based on [Ivan Tikhonov's captcha library](https://github.com/ITikhonov/captcha). Usage ----- Add `ecaptcha` as a dependency to your project's rebar.config: ```erlang {deps, [ecaptcha]}. ``` Then use one of the API functions to generate the image and short random text: ```erlang {Phrase, PNGImage} = ecaptcha:png( 5, #{effects => [line, blur, filter, dots, reverse_dots], color => black, alphabet => latin_uppercase, font => <<"dejavusans">>} ). ``` `PNGImage` can be sent to the user with `Content-Type: image/png` and user have to guess the 5-letter `Phrase` which is printed on the image. `effects` option defines a set of different effects, which suppose to make it more difficult to recognize the text with OCR systems: * `line` - draws a curved horisontal line on top of the text * `blur` - blurs the image (averages each pixel's color with it's neighbours) * `filter` - makes letters hollow * `dots` - draws 100 random 2x2 white dots on top of the image, effectively removing small patches from it * `reverse_dots` - draws 20 random dots of a randomized size from 1 to 3px using a color opposite to the current color (so, reversing the color - black becomes white, white becomes black) The more effects you apply, the more difficult it is to recognize the text on the image (for both human and OCR). `color` option defines the image's color. It doesn't affect Captcha strength, but can be used to match your website / app style. You can select from a set of predefined colors: `black`, `red`, `orange`, `blue`, `pink` or `purple`, or it can be provided as a 3-tuple `{Red, Green, Blue}`, `0..255`. `alphabet` defines the set of characters that can be printed on the image. It can be one of the predefined sets: `numbers` for 0-9, `latin_lowercase` for a-z, `latin_uppercase` for A-Z or it can be a binary containing all the allowed characters (duplicates are ok), eg `<<"1234abcd">>`. `font` binary name of one of the supported fonts. Function `fonts/0` can be used to get the list of available fonts. Fonts are pre-rendered at NIF compile-time, see the `c_src/fonts.h` and `FONTS` parameter in `c_src/Makefile`. All the options are optional. ```erlang ecaptcha:gif/2 ``` Same as `ecaptcha:png/2`, but returns the image encoded in GIF format. `Content-Type: image/gif`. ```erlang {Phrase, Pixels} = ecaptcha:pixels(5, #{font => <<"ubuntu-r">>, alphabet => numbers}). ``` `Phrase` is the same as above, but `Pixels` is a `200x70 = 14000` bytes binary of greyscale pixels, from top-left to bottom-right, line-by-line. It can be used to, eg, display pixels with JavaScript on a `