Atlassian Bitbucket supports diff view for commits also supports comparing before and after of images. This is very useful to see how your images are affected by image optimization tool. How fast a web site is loaded is very important for good user experience. Even Google’s search engine checks sites response times and gives priority to fast sites. To take advantage of this, you have to optimize your image files, but too much optimization may also reduce quality of images. Most image optimization tools allows you to adjust level of quality you want to trade for image size. After optimizing you may want to check how you images are look compared to previous version. With Bitbucket this is very easy, just commit your changes, push to Bitbucket and in diff view you can view how your images are affected using 3 different comparison method as shown in the following screenshot.
Side by side view is my favorite but blend and split are also very good.