applescript not counting images in a Pages document

I'm trying to delete all the images in a Pages document using Applescript. The document was created by pasting an online chat transcript into a blank Pages document. I now want to strip out the avatars. I'm new to applescripting in Pages and have a simple script:

tell application "Pages"

activate

tell front document

get the count of images

end tell

end tell

which i thought should tell me how many images were in the document. It works with some other Pages documents, but not this one:

Dropbox - test.pages

(I've abbreviated the actual transcript!). Please can anyone tell me why the count is zero?

Apologies if this is the wrong Community.