**Other customers on O2 Payg / MVNO won't benefit from this trick**
If you're on O2 or GiffGaff with a decent mobile device, you might notice sometimes webpages rendered on mobile data looks a bit off / pixelated, especially when the images are being zoomed in. Or sometimes the background gradient colours looked really off.
This is likely caused by the image compression proxy that O2 deployed between you and the internet. I have not done an extensive test on this subject, but .jpg and .png files are notoriously heavily compressed when they're being sent through the mobile network.
To test if the page quality is affected by the O2 image compression, there are few things you can do:
(1) Find a NON-HTTPS site with .jpg images, online albums like imgur should do.
(2) CLEAR CACHE of browser, this might involve wiping all app data. Alternatively you can use Chrome incognito mode throughout.
(3) Browse to the selected URL over mobile network, save a picture to the device.
(4) Clear Cache / open another Incognito tab, download the same picture to device.
(5) Open Gallery / Photos app and compare the two images.
In order for this test to be accurate, it's best to try different sites with different types of images, including .gif, .jpg, .png, etc.
If you noticed difference in quality between the two images, then your device is suffering from O2's Image Compression.
If you're lucky enough to an O2's pay monthly customer, you can try setting up the following APN, do a REBOOT, then test again.
Name: o2 bypass
Proxy: Not set
Port: Not set
Server: Not set
MMS Proxy: 126.96.36.199
MMS Port: 8080
Authentication Type: PAP
APN Type: default,supli
APN protocol: IPv4
APN roaming protocol: IPv4
MVNP type: None
Please note this APN seem to be quite temperamental, it works for me sometimes but not all the times. However if O2 image compression is a thing you wanted to get rid of, it's definitely worth a try.