i have found its got nothing to do with opera, all browsers give poor imagery if you connect your phone with net access to your pc.
supposedly it has more to do with O2 and your provider of choice only allowing low res images! click here
surely that defeats the purpose of 3g and its high speed equivalent?! some users have found third party software (depending to their provider of choice) to give pages with high quality images, but there doesnt seem to be anything for o2. i seem to be stuck with only using IE, and hitting CTRL+F5 on every single page to improve overall image quality!