acha-framework/src/frontend/core/scripts/directives/captcha/template.html

is a modular framework on both client (angular.js) and server (node.js) side, it provides security, orm, ioc, obfuscation and ...

<div class="af-captcha af-component">
    <input type="text"
           ng-model="model.value"
           number-only
           maxlength="4"
           ng-readonly="vm.waiting">
    <img width="80" height="30" ng-src="{{vm.image}}" />
    <button ng-disabled="vm.waiting"
            ng-click="vm.refresh()">
        <i class="fa fa-refresh"></i>
    </button>
</div>