Unable to filter/block image for mime type avif/webp

[Pratik]

Image analyzer does not scan images that are of avif and webp image format.
Inappropriate images in avif/webp format sidesteps Image analyzer.

But instead of avif/webp images, we can request to remote server jpg/png image format which is scanned via image analyzer.
Content modifier can rewrite clients' request headers.
Below is an example request headers received from client:

GET /photo-1653794719441-350f63d49de2?ixlib=rb-1.2.1&ixid=MnwxMjA3fDB8MHxwaG90by1vZi10aGUtZGF5fHx8fGVufDB8fHx8&dpr=1&auto=format%2Ccompress&fit=crop&w=1599&h=594 HTTP/1.1
Host: images.unsplash.com
User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:101.0) Gecko/20100101 Firefox/101.0
Accept: image/avif,image/webp,*/*
Accept-Language: en-US,en;q=0.5
Accept-Encoding: gzip, deflate, br
Referer: https://unsplash.com/
Connection: keep-alive
Cookie: <cookie>
Sec-Fetch-Dest: image
Sec-Fetch-Mode: no-cors
Sec-Fetch-Site: same-site
Pragma: no-cache
Cache-Control: no-cache

Content modifier rewrites client headers and instead of avif/webp image, it requests remote server for jpg/png image.
Below is the example for request headers after it has been rewritten by content modifier.

GET /photo-1653794719441-350f63d49de2?ixlib=rb-1.2.1&ixid=MnwxMjA3fDB8MHxwaG90by1vZi10aGUtZGF5fHx8fGVufDB8fHx8&dpr=1&auto=format%2Ccompress&fit=crop&w=1599&h=594 HTTP/1.1
Accept: image/png;q=0.5,image/jpg;q=0.5,*/*
Accept-Language: en-US,en;q=0.5
Cookie: <cookie>
Sec-Fetch-Dest: image
Sec-Fetch-Mode: no-cors
Sec-Fetch-Site: same-site
Pragma: no-cache
Referer: https://unsplash.com/
User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:101.0) Gecko/20100101 Firefox/101.0
Accept-Encoding: gzip, deflate
Host: images.unsplash.com
Connection: keep-alive
Keep-Alive: timeout=6

For validating the policy you can visit https://unsplash.com/ which requests images in avif format.

image.png (614.37 KiB) Viewed 991 times

But with content modifier, the client requests images in jpg and the server responds with jpeg which is scanned by Image analyzer.

image.png (844.67 KiB) Viewed 990 times

Use the below-Rewriting policies to achieve the same.

Slide1.JPG (83.12 KiB) Viewed 899 times