WebMaestro.Fr

Upload the layers of your image, and create a parallax effect !
It works great on smart devices too !
The first step is to create with your favorite picture editing software (Photoshop, GIMP…) an independent image for each ground composing your image. All these layers shall be the same size, and should be in .png format as they are meant to include transparency areas. 
Then, on your post editing page in WordPress, click the Insert Media button, and (the same way you would create a gallery) upload your layers under the Create Parallax item. Reorganise the layers if needed, from the background to the front. 
You can finally configure the animation (calibrate, invert, limit, scalar, friction), and publish !
There is <a href="http://webmaestro.fr/image-parallax-plugin-wordpress/" rel="nofollow ugc">some examples</a> on the plugin page.
It uses <a href="http://wagerfield.github.io/parallax/" rel="nofollow ugc">parallax.js</a> by Matthew Wagerfield.

Image Parallax

Create images with a parallax effect. Upload some layers, configure the animation, and publish !

adamrob

Parallax Scroll; the easiest way to get a parallax scrolling background image for an element on your page/posts.
Examples include:
<ul>
<li>Create a header text with a parallax scrolling background.</li>
<li>Create a full section containing any content with a parallax scrolling background.</li>
<li>Give single elements of your pages a parallax scrolling background.</li>
<li>Ideal for sites with sections.</li>
</ul>
How?
<ul>
<li>Simply create the content required in the custom Parallax Scroll post type.</li>
<li>The Parallax Scroll admin page will display the shortcode required for all Parallax Scroll post types defined. Copy this shortcode, and paste it into any page or post.</li>
<li>Alternatively you can use the plugin directly in your php code. Implement it straight into your theme!</li>
<li>Thats it!</li>
</ul>

Parallax Scroll by adamrob.co.uk

Create a header, or custom post/page with a scrolling parallax background. All with a simple shortcode.

Image Parallax vs Parallax Scroll by adamrob.co.uk