The thumbnails are quite low resolution. We can likely afford to make them higher quality. In addition, we should consider:

• clicking to expand to larger viewer
• increasing size on the page (may need to also reduce padding between thumbnails)

These images come from Speedline and are then shrunken. With a default configuration, the scaling rate I saw was 2.2x. We can achieve this much increase in fidelity without making any changes to Speedline.

The images are also jpeg, which isn't ideal. We re-encode the scaled down image data in the audit using jpeg-js just because it's the only encoding library we have on hand that'd work in Node and the browser (otherwise we could use canvas to encode webp...). Not sure what the image encoding is from Speedline directly (it's probably whatever is in the trace snapshots, but I don't even know what that would be). (EDIT: speedline uses jpeg-js too. Changing this seems like it'd be not trivial)

related (kinda): #9204 (comment)