ShortPixel
ShortPixel is an awesome way to reduce your images
ShortPixel is a great service for anyone looking for an easy way to compress images. Why compress images? If you maintain a blog or host websites, a good image compression tool can make the site load faster. In addition, smaller image sizes mean less disk space.
If your uploading images to Slack, a better-compressed image may help slack show an inline preview on those larger animated GIFs.
To use the site, simply create a free account and then drag and drop images to the compression optimize box on their website. Developers will be happy to know that there are API tools for PHP and a command line tool.
Website Description
ShortPixel algorithms were perfected while optimizing over a hundred and a half million real-life images. ShortPixel not only offers the best compression for JPEG, PNG, GIF and PDF files but it also saves you a lot of time. After the simple installation, ShortPixel makes sure that all the images on your site are immediately optimized after upload.
While ShortPixel promotes the use of the WordPress Plugin and API, you don't need it to use their compression technology.
https://shortpixel.com/online-image-compression
Sample Compression
This animated gif was originally 3.6 MB, and now it's 1.6 mb.
I compressed an old PDF file from 6MB to 795K. Check out the PDF to see if there's any serious quality lost: http://www.cryan.com/pdf/IncredibleUniverse.pdf