for a gallery:
[mesa_lightbox_image image_url="http://demo.mesathemes.com/wp-content/uploads/2014/05/blog_post_placeholder.jpg" thumb_width="" title="Image" caption="description" gallery_name="gallery" class=""]


for a single image lightbox:
[mesa_lightbox_image image_url="http://demo.mesathemes.com/wp-content/uploads/2014/06/blog_post6_placeholder.jpg" thumb_width="" title="Image" caption="description" gallery_name="" class=""]