Message Editor Interface settings?

[Howard]

OK after a bit of mucking around, I have found this.
If I "post reply" to this thread we are actually looking at now, my interface looks like this:
editor 3.jpg
So images are attached using the (paperclip) "Attachments" button.
However, on SOME threads when I hit the "Post Reply" I get a slightly different interface, thus:
editor 2.jpg
This one has an additional button, the "Insert Image" button where I can link to an image on another web site such as Photobucket or even Shedfull. But this button does not appear when I reply to some threads, this one we are reading now, for example.
editor 4.jpg