10 Best Image Optimization Plugins for Speeding Up WordPress
Optimizing your images not only helps your WordPress site load faster but can also boost your SEO.
WP Smush

WP Smush is a WordPress plugin that allows you to optimize images without losing quality.
With WP Smush, you can set up automated smushing so all of your new images are automatically compressed when uploaded to your site. WP Smush is also compatible with NextGEN Gallery and WP Retina 2x for high quality image display with the smallest possible file size.The plugin work by stripping meta data from JPEG files, optimizing JPEG compression, converting certain GIFs to indexed PNGs and stripping the un-used colors from indexed images.
For beginners, it is an easy and simple way to optimize their images and improve their site performance.
WP Smush gives you no control on how much you can optimize an image. While it does reduce the image file size, it is not the best solution.
EWWW Image Optimizer

EWWW Image Optimizer is a WordPress plugin that optimize your images as you upload them. You can also optimize your previously uploaded images. It also allows you to convert file format, so that you can choose a format that gives a lower image size. It can also optionally apply lossy reductions for PNG images.
SEO Friendly Images

SEO Friendly Images edits all your images with proper ALT and TITLE attributes to help boost your SEO. If your images don’t have ALT and TITLE already set, this plugins adds them in according to the options you set
If you have a lot of un-optimized images on your blog, it’s time to use this plugin to optimize it.
Hammy

Hammy takes your regular content images (only within posts and pages, not custom post types) and regenerates a number of smaller sized images. When a person visits your website, it then automatically provides them with the most appropriate image . This makes for a better experience, especially on mobile. This uses the new WP 3.5 image code.
Hammy only works for images within posts and pages, not custom post types.
Imsanity

Uses WordPress built-in image scaling functions
CW Image Optimizer

The CW Image Optimizer is a WordPress plugin that will automatically and losslessly optimize your images as you upload them to your blog. It can also optimize the images that you have already uploaded in the past.
PB Responsive Images

Media File Renamer

The Media File Renamer is a WordPress plugin that physically renames media files nicely for a cleaner system and for a better SEO.
This is originally an automatic renamer based on the Media title. This plugin features were all meant to be automatic depending on the title of the Media.
Lazy Load
BJ Lazy Load