SOME pictures been blocked in vista explorer right pane

"Trying to live without "View as Web Page" in vista explorer ...
When viewing an .HTM in the right pane vista explorere says:
"SOME pictures been blocked te help prevent the sender from identifying your computer. Opne this item to view the picture."
Does that mean that SOME other pictures are not blocked?
Which are, which aren't?
Where is that documented.
Regards,
Coen

I think personally that it is a real explorer bug.
The explorer is depending from too many applications (ie, windows mail applications, etc...). Some people having the same problem solved it through Outlook???? So maybe some registry keys are shared for this particular case.
I remember having a lot of problems of this type in XP, that is why i decided not to use anymore the explorer which i substitute with freecommander.