we don't have any control over the thousands of images linked from off site.
You dont have any control over hot-linked images on your site other than to continue allowing them to be hot-linked, or blocking them entirely. If you continue to allow them to be hot-linked using their http address, you could set your .htaccess file to be less-strict and allow those items of a certain file type, or from within a certain path. Or you could set your .htaccess to just forward all http page requests to https pages, still allowing all media to be accessible through their http... and https addresses.
Any suggestions about these (short of going through 2 million+ posts)?
As detailed within the very first post of this thread, use the SQL commands to find all occurrences of (for example) "http://pianoworld.com" and replace with "https://pianoworld.com". The process takes less than an hour to complete. Backing-up your database is where the majority of your time will be spent.
