omerk

<a href="http://fancybox.net/" rel="nofollow ugc">Fancybox</a> is a tool for displaying images, html content and multi-media 
in a Mac-style “lightbox” that floats overtop of web page. It was built using the jQuery library.
This plugin inserts the necessary elements required to run Fancybox on your blog. It also groups 
images within posts using rel attributes. (Based on the code found on <a href="https://wordpress.org/support/topic/automatic-adding-lightbox-rel-and-group-to-images-in-posts" rel="ugc">this</a> 
forum thread)
To disable Fancybox per post: Add a custom field called ‘nofancybox’ and set it’s value to ‘true’. 
Instructions on how to add custom fields to posts can be found at <a href="https://codex.wordpress.org/Custom_Fields" rel="nofollow ugc">this</a> 
codex article.

Fancyboxify

This simple plugin enables Fancybox on image links. It groups all images within a single post and can also be disabled per post.

DaganLev

huntlyc

Simple, easy to use, fancybox style popup.
Works for all images in your page that are in anchor tags. If it finds more than one, it will create a small gallery you can navigate through with the buttons or your keyboard. Advanced users can open iframes and html content in it fairly easily.
<h4>Avanced users</h4>
<h4>Basic use</h4>
Anchor class for popup: “hs-rsp-popup”
<h4>Advanced use</h4>
<ul>
<li>disable gallery feature and popup for image by adding this class: no-hsrsp-popup</li>
<li>anchor classes for iframe popup “hs-rsp-popup iframe”</li>
<li>anchor classes for html popup “hs-rsp-popup hiddendiv”</li>
</ul>
<h4>Examples</h4>
To popup an image give the anchor tag around the image this class: “hs-rsp-popup” 
Example: <code><a href="image.png" class="hs-rsp-popup"><img src="image.png" alt="image"/></a></code>
For an iframe, set the srct of the iframe and use the class “iframe” combined with “hs-rsp-popup”: 
 <a href="http://www.youtube.com/watch?hl=en-GB&v=2WNrx2jq184&gl=GB" title="Bird is the word" rel="nofollow ugc">Watch this</a>
You can also use this to show html content. For local content just use the id of the element for the href: 
 <a href="#elementid" rel="nofollow ugc">click here</a> 
 Hello, World!
For remote content, link to the page, for example: 
 <a href="http://www.hotscot.net" rel="nofollow ugc">click here</a>
<h4>Setting Popup Size (image/iframe)</h4>
You can use the following html5 data attributes in your link to set the size: <code>data-popupheight="100" data-popupwidth="300"</code> These values are in pixels.
For Example: 
 <a href="image.png" rel="nofollow ugc"></a>
Note: for this to work, you have to use both the data-popupwidth and data-popupheight attributes.

Really Simple Popup

Simple, easy to use, fancybox style popup

Fancyboxify vs Really Simple Popup