Here's the story on where the image is stored, based on a single test. Start at the bottom and work up:
geo w pic.pages is a small wp file with a single image—the 48 KB gif file I dragged onto it from the internet.
geo no pic.pages is the same file, saved after the picture had been deleted. Note the 228 KB reduction in size.
geocache.gif is the image, saved directly from the webpage.
geocache.pdf is the same picture, selected and copied from the pages document, then placed in Preview using command-N (New document from Clipboard). Preview opened it as a PDF file, and I saved it from there.
Jump to the top of the list.
Pages files are zipped archive packages, which can be expanded after changing the extension from .pages to .zip.
The package contains a jpg thumbnail and a pdf image of the document in the Quicklook folder, an xml index file (making up the bulk of the document) and the image, stored in TIFF format.
Total size: About 630 KB (the Quicklook files take about 100 KB), compressed in the final package to 288 KB.