jquery Multi file upload preview
http://www.fyneworks.com/jquery/multifile/#Usage
http://www.raymondcamden.com/2013/09/10/Adding-a-file-display-list-to-a-multifile-upload-HTML-control
http://www.formget.com/upload-multiple-images-using-php-and-jquery/
CAPTCHA php
http://www.codeproject.com/Articles/26595/CAPTCHA-Image-in-PHP
https://ellislab.com/codeigniter/user-guide/libraries/file_uploading.html
http://www.tutorialchip.com/php-upload-class/#tab-download
http://www.heylove.de/
http://jindo.dev.naver.com/smarteditor/user_guide/