Elixir CI


Finger is a verification library - captcha - to prove hommaannnnnness of a user.

Finger achieves this by showing pictures of N hands holding up random fingers and asking users to verify how many fingers am I holding up, which is a task our machine friends suck at!

{answer, image} = Finger.generate(N)
  • answer is the string answer to the challenge
  • image is the binary challenge image to be displayed to the user

You can see the Finger output with the following examples. Please not that rest of the form fields are generated by the application not the library.

Example 1

The answer would be 2025

Example 2

The answer would be 2543

Context and Demo

** Please do not sign up if you do not intend to pass the email verification :)


This library requires the awesome imagemagick software to be installed on your machine. It is not version dependant.


Lot's of imporevements to be made to the library itself. First elixir and hex package, please bare with me :)

  • Maybe fetch the asset paths once rather than everytime?
  • Error case improvements
  • unit testing System.Cmd
  • unit testing Docs


Install from Hex

def deps do
    {:finger, "~> 0.1.3"}

Getting Started

  1. Create an action to display the image
defmodule Elxsy.TestController do
  use Elxsy, :controller

  def test(conn, _params) do
    render(conn, ....)

  def finger(conn, _params) do
    {answer, image} = Finger.generate()
    # store the answer in session or somwhere else on the server side
    |> put_session(:fingers, answer) 
    |> put_resp_content_type("image/jpeg")
    |> send_resp(200, image)

  def verify(conn, params) do
    answer = get_session(conn, :fingers)
    delete_session(conn, :fingers)
    if params["fingers"] === answer do
  1. Add to your routes
    get "/test/finger.jpg", TestController, :finger
  2. Add to your template for test action
    <img src="<%= Routes.test_path(@conn, :finger) %>" />
    <input type="number" name="fingers" placeholder="Please tell me how many fingers are shown in each hand" required="true" />
  3. Verify for the answer in form submission with the verify like the example.


Documentation can be found within the code and methods itself as well as hexdocs but the important highlight.

Default number of images is: 4
Minimum number of images is: 2 (inclusive)
Maximum number of images is: 9 (inclusive)

Contribution to the library

Please fork and make necessary changes, raise a pull request.

Contribution to the picture stack

More the merrier!

  • Fork the project
  • Please take a SQUARE picture of your hand holding some fingers up - respectfully
  • Either facing your palm or back of your hand
  • With decent lighting and exposure
  • On a mixed background like nature or some furniture with patterns. Please avoid clear, flat walls and plain backgrounds.
  • Resize to 200x200
  • name the picture as {finger_count}_{YYMMDD}_{github_username}.jpg ie, if I am showing 2 fingers up, it would be 2_210408_ykurtbas.jpg
  • commit into assets folder
  • Raise a pull request.

Bugs or Issues

  • Please raise a bug or issue request in the tracker