Enhancement request: Cache baseline and actual images

[monkpit]

I have my pages set up to take screenshots with a page height of 10,000 px. The generated PNG files are ~10mb. As I click back and forth between baseline and actual in VisualReview, I noticed that there was a considerable delay. After opening the network tab, I realized that each image is loaded / reloaded from the server each time I click the radio button for baseline / actual.

Ideally, the UI should be written in a way that it does not need to make a request out to the server every time, or the cache headers should be set to allow the browser to cache the images.