chebum

<a href="http://visualwatermark.com/wp-photo-protect/" rel="nofollow ugc">Photo Protect</a> adds an invisible layer over your post images to protect them from copying. 
Visitors trying to save an image will get a blank image instead of your photo.
Here is why you should download it:
<ul>
<li>Protects your images. 9 out of 10 visitors won’t be able to download and copy your images.</li>
<li>Works in every modern browser. No plugins required!</li>
<li>Has no dependencies. Correctly works with every framework your theme may have jQuery, MooTools, ExtJS, GWT, etc.</li>
<li>Supports responsive themes. Applies protection in a way both theme and protection layer continue to function properly. Even if your visitor resizes her browser.</li>
<li>Works on smartphones.</li>
</ul>

Photo Protect

Adds an invisible layer over your images to protect them from copying.

dFactory

<a href="http://www.dfactory.co/products/image-watermark/" rel="nofollow ugc">Image Watermark</a> allows you to automatically watermark images uploaded to the WordPress Media Library and bulk watermark previously uploaded images.
For more information, check out plugin page at <a href="http://www.dfactory.co/" rel="nofollow ugc">dFactory</a>, <a href="http://www.dfactory.co/docs/image-watermark/" rel="nofollow ugc">documentation page</a> or plugin <a href="http://www.dfactory.co/support/forum/image-watermark/" rel="nofollow ugc">support forum</a>.
<h4>Features include:</h4>
<ul>
<li>Bulk watermark – Apply watermark option in Media Library actions</li>
<li>Watermark images already uploaded to Media Library</li>
<li>GD LIbrary and ImageMagic support</li>
<li>Image backup functionality</li>
<li>Option to remove watermark</li>
<li>Flexible watermark position</li>
<li>Watermark image preview</li>
<li>Set watermark offset</li>
<li>Select post types where watermark will be aplied to uploaded images or select adding watermark during any image upload</li>
<li>Select from 3 methods of aplying watermark size: original, custom or scaled</li>
<li>Set watermark transparency / opacity</li>
<li>Select image format (baseline or progressive)</li>
<li>Set image quality</li>
<li>Protect your images from copying via drag&drop</li>
<li>Disable right mouse click on images</li>
<li>Disable image protection for logged-in users</li>
<li>.pot file for translations included</li>
</ul>

Image Watermark

Image Watermark allows you to automatically watermark images uploaded to the WordPress Media Library and bulk watermark previously uploaded images.

Photo Protect vs Image Watermark