This is getting interesting. I finally found an explanation I can accept:
If (…) the owner of a website uses in-line linking to display an image rightfully posted on another site, the courts have held that no copyright infringement has taken place. –IT Law Wiki
Like other Wikis, this can not be treated as 100% reliable source, but it pretty much summarize what many other sources say less clearly.
And since in-line linking has happened inside MyOpera server, it is also not "hot linking" in the sense as it is usually understood. There's no bandwidth used any more than me displaying the same image anywhere else around MyOpera. Moreover, there's no risk that the author (me in this case) would replace the image with malicious content since each image gets unique address at MyOpera albums and can't be switched into another by client.
This means I owe an apology to Salim Akhtar for accusing him on copyright infringement, and to MyOpera admins for wasting everyone's time 😮