1) Each blog should have this Enable Media Replace plugin installed - BUT not activated. SKIP to Step 2
2) Go to Plugins, find Enable Media Replace and click ACTIVATE
3) Unzip images and/or locate image folder for the assigned blog.
You should use the same images with the file names for replacement, If the file names are not exact, the replace function will not work.
4) For EACH missing image (you'll know from the broken image icon). You'll repeat these steps