Recently I have been looking for ways to block images from being loaded. There are some extensions on Firefox, but it can be difficult maintain the same extensions on browsers in different qubes. This is also a solution only relative to the browser.
In the bigger picture, it would be more optimal to configure a net-qube to drop all the requests matching a media Content-Type header such as “image/jpg”. I looked at qvm-firewall, but it seems to be more relevant to the IP protocol being used rather than the contents of a packet.
The sys-firewall and sys-net qubes will not see your traffic at all, if you use https (and you should use https). They may only see where you’re connecting but not what you transfer.
You can’t do that on https traffic because it’s encrypted. You may try a http proxy but it won’t look at https traffic content either, nowdays most traffic SHOULD be https so I think it’s a dead end for you.
Use a proxy like Squid in MITM mode.
Configure the ACLs in Squid to run content filtering - this is well
documented.
At this stage you have offloaded all the filtering and certificate
checking to the proxy - not so bad since you have total control over
the system.
You could use a DNS blocking tool like uBlock for the browser and use the “element picker mode” to create rules for certain image urls or you use something like pihole as firewall qube in between to archive the same.