Special thanks to http://extensionizr.com/ Chrome extension template builder
Install
Go to chrome://extensions/ inside Google Chrome
Drag and Drop /bin/Kato-Gif-Hider.crx anywhere on the page
(since Chrome no longer allows extension installs direct from the web, you may see a few warnings. Just download the .crx file, open in Finder, and drag onto extensions page)
Hide Image
Click image to trigger message collapse
(Yes, I know there is a tab at the top right of each message, but I find it very cumbersome and need to close A LOT of GIF's throughout the day.)
Hide all by Category
Hover over top left of page to open flyout
Click category to collapse messages of that type