Originally Posted by macropod

In your Excel workbook, instead of (or as well as) the pictures, insert their filenames.

Then, in Word, insert a field coded as:
{IF {INCLUDEPICTURE {IF TRUE "C:\Users\My Document Path\Pictures\«Image»"} \d} {INCLUDEPICTURE {IF TRUE "C:\Users\My Document Path\Pictures\«Image»"} \d}}
where 'C:\Users\My Document Path\Pictures' is the path to those pictures and '«Image»' is a mergefield that points to whatever name you give the heading row that contains the image filenames. The filepath is probably something like:
C:\Program Files\Microsoft Office\MEDIA\CAGCAT10
You can find the correct path for a given image via Insert|Clipart, selecting an image then choosing 'Properties'.