My apologies for the previous incomplete answer ... this miserable web
interface isn't my usual environment.

If the document will be used only to print on paper and not sent to others,
then link the pictures instead of embedding them. In the Insert Picture
dialog, after selecting the file, click the down arrow next to the Insert
button and choose Link. That will insert only a field in the document, at
most a few dozen characters. The document will display and print the picture,
but the graphic data will stay in the picture file.

If you have to send the document out, although it's theoretically possible
to link the pictures and send both the dicoument and the picture files,
there's a problem. The pictures would have to be in the same folder location
on the recipients' computers as on the original so the links wouldn't break.
That can be hard to do, so it's better to embed the pictures in the document
(ordinary Insert does that). To keep the document size to a minimum, take the
picture files into a real graphics editor (such as the free IrfanView,
www.irfanview.com) and resize them to their final size, resample to a
reasonable resolution (96 dpi for screen viewing, 150 dpi for printing), and
do any cropping or contrast/brightness adjustments. Insert only the final
file into Word, and don't do any manipulations there other than positioning.