Lighthouse fails to flag a 24MP image

[patrickhulce]

Provide the steps to reproduce

1. Run LH on https://www.portuguesetrails.com/en
2. Observe the horrifying 33 MB of images it loads
3. Look through all the image opportunity audits for their whopping 24 megapixel image https://www.portuguesetrails.com/sites/default/files/gallery/iStock-621859064BicicletasPraia_AG_PT_moedas1.jpg whose dimensions are 6000x4000

What is the current behavior?

Lighthouse does not flag this image as being massive.

What is the expected behavior?

Lighthouse flags this image.

I'm not really sure what to specifically do about this one though. It falls through the cracks because...

• It passes optimized images because for a 24MP image, it is fairly well compressed at only 2 MB.
• It passes webp images for the same reason.
• It passes "use responsive images" because it is offscreen and has client dimensions of 0.
• It passes "use offscreen" because it is requested after TTI.

I don't really want to change any of those constraints in our existing audits, so it feels like there's just a hole in our coverage for "this image is just way too big".

Related issues
#7173

[patrickhulce]

We decided to count images that are offscreen in the "use-responsive-images" audit with an assumed display size of the entire screen.