I have a large document (>1000 pages A4) with several tens of images and other illustrations.
Is it possible to have all these images and illustrations moved (or exported, or detached; or whatever you’d call it) to seperate files in the same directory as the main document, leaving the link in the odt-file?
This should lower memory consumption and would make it more easy to eventually connect the text file to a Scribus file (or other system).
How are your images presently inserted in the document? Have you pasted them? Have you Inserted>Image with which options (access to file or link)?
When you insert an image, you can choose between embedding it or linking to the file. But you can’t change this afterwards.
Don’t forget to mention OS name, LO version and save format (.odt or .doc(x)).
All the current images are pasted in the document, resulting in a document of around 40 Mbyte. Mind you, it’s not because of the illustrations, the size mainly comes from the 1000+ pages A4 of text currently in the text.
But I’d like to move the illustrations outside the main document and only keeping a link to the illustrations.
Pasting embeds the images in the document. Unfortunately you can’t “convert” from embed to link. You must remove the images and re-Insert>Image choosing the link option.
Regarding your document size, following a strict styling method dramatically reduces file size. Chase direct formatting and replace it by ad-hoc style application. Caution! M$ Word conditioned us into direct formatting (DF) for anything else than paragraph, e.g. bold or italic. Instead, use character styles like Emphasis for italic and Strong Emphasis for bold. Thus, you have a single definition and multiple usages. With DF, each occurrence is its own definition and single application occurrence. Same for pages and lists.
You didn’t answer for OS and LO version. Most importantly, you didn’t disclose your save format. If it is .doc(x), no luck. Your document will remain 40 MB because the format has no character, page, list, … styles.
About OS and LO: it’s Kubuntu / Linux and my LibreOffice 25.2.0.3
I’ll try to follow your suggestion on using character styles instead of direct formatting. It’s the first time in many years I’ve been given this suggestion, but it seems very useful.
Though I’ve been using Word about 4 decades now (and LO Writer about 15 years), I prefer LO. On the other hand, I’ve never made a M$ Word document larger than about 100 pages, so the problems I’m experiencing with LO don’t occur in M$ Word.
(And I like the dollar sign you use 
thus, this pretends it can : Extract embedded images and replace embedded images with linked images: PicExtract | Apache OpenOffice Extensions
trendy these days : How to compress multiple images?
Yes, this extension does that. Its LibreOffice counterpart warns:
LO6.1 and higher: ALL images will be extracted!
Replacing embedded images with linked images
not possible.
So what is your point?
PicExtract.vba ?All those points sound reasonable.
Yes, but it uses the ODF version 1.2.
background details : Insert image into LibreOffice as Link using API/Macro - Stack Overflow
this one seems to be the (painful) way : Replace an image using a macro - #11 by KamilLanda
seems almost easier to directly hack Pictures/ and content.xml in the zip archive 