No doubt the admin will check this out, I can certainly see the button, but I don't know if it has just appeared, I never use it anyway.
WH-- looks like you've embedded an image, rather than used the Postimage 'add image' feature. You can still do that with any image library, including Postimage, I do this myself, to bypass the 'thumbnail linked to heavily laden with inappropriate advertising' image on Postimage.
There's some tips here, showing how to get around the thumbnail display.