just add your thumb image according to the following form...
<img src="address of your thumb" class="galleryimg" title="here input caption of your image" data-file-url="address of big image" data-file-width=" width of the big image" data-file-height="height of the big image"/>
add in section <head>
easygallery.jseasygallery.css- and jquery library http://code.jquery.com/jquery-2.1.0.js