Word export fails to export attached images

Hi folks,

our Confluence installation fails to export images which are stored as attachments with the individual Confluence page:

• Images are "exported" into just blank boxes.
• Thumbnails are exported into links (though no image appears in the actual Word document either).

Anonymous users are not allowed to browse our Confluence installation ("Anonymous access" is disabled).

I can provide screenshots of the actual page in Confluence and a sample export Word document if needed (I haven't added them yet because I'd need to revise the Word document to remove sensitive information).

This is a serious thing and we cannot effectively use the Word export. Please help. Thanks in advance.