[aedis]

This is probably CopyTrack. They have hidden 1px tracker jnside email. These are extortion tactics.

I dealt with them before. Just ignore them and stop opening email. They asked 800 euro for 2 small images. Since a OP is in UK the tought they can do triple price.

[bmacho]

They don't see if you open your email or even if you download and open the attachments, at least in any sane email client. If your email client sends reading information back then you should replace it instead of not clicking on emails.