Wonderm00n

The WordPress default galleries always link to the full image size which can be pretty annyoing because most users upload huge pictures.
With this plugin you can set a default size for the galleries to link to. This can be thumbnail, medium, large or full.
For now this a global setting for all galleries, but on a future version I plan to let you choose a specific size for each gallery you create on your WordPress posts or pages.
It’s also possible to add arguments to the link (A) tag. This may be useful to add lightbox/fancybox script compatibility.
Based on the oikos.org.uk solution that can be found at http://oikos.org.uk/2011/09/tech-notes-using-resized-images-in-wordpress-galleries-and-lightboxes/

Wonderm00n's Gallery Link Size Changer

This plugin allows to change the way the Wordpress gallery links. You can select to…

Francesco Sganga

Optimize images (jpg, png) in your WordPress site by converting them to .webp extension (it uses PHP GD library) 
WP Media Optimizer (.webp) only works with Firefox and Chrome (at this time).
— SAFARI NOW SUPPORTS .WEBP images —
Now with LAZY LOAD FEATURE!
IMPORTANT: WPMOWEBP works only in the frontend side of your website (e.g. not in wp-admin/)
ABOVE THE FOLD Feature is not really “for dummies” but with some tests you can really improve your PAGE SPEED RATE! Hope you can appreciate this feature.
USAGE
Simply install and activate it, and your images will be optimized.
You can send a Feature Request from the Plugin Settings Page. 
I hope you will use this form so I can add new features to this simple and wonderfurl plugin!
You can enable the new Lazy Load Feature by making a little donation to the author, you will receive a life time token for this feature and future improvements.
HOW IT WORKS
When anyone access to a WordPress page, plugin check for images already converted to .webp. 
If one or more images have not been already converted, the plugin converts them immediately. 
Converted images are stored in a subfolder of wp-content folder: wp-content/wpmowebp
TROUBLESHOOTING
If WordPress go out of memory try to add 
define(‘WP_MEMORY_LIMIT’, ‘256M’); 
to your wp-config.php
Enjoy your new WordPress Plugin.

WP Media Optimizer (.webp)

Automatically optimize images in your Wordpress site by converting them to .webp extension

Wonderm00n's Gallery Link Size Changer vs WP Media Optimizer (.webp)