Is there any way to re-size the image used with the Image Annotation plugin? Currently it uses the fullsize derivative, but these images are too big form my item/show page. If there is no way to re-size the images, would there be a way to link to an annotated image on it's own page?
This won't affect your already-uploaded images, but do remember that you can change the size of the "fullsize" images Omeka generates with the "Fullsize Image Size" option in Site Settings.
I've made the change you suggested and reduced the dimensions of the "fullsize" images Omeka generates. However, I am still stuck with 500+ really large images that were previously created. But I think I've found a quick way to reduce these image sizes as well. I've made a copy of these "fullsize" files onto my computer, and I have batch resized them using the Microsoft Powertoy Image Resizer.
When I first tried to move these reduced image files to the omeka/archive/fullsize folder I got an error message saying the files could not be copied. However, I realized if I deleted the old large files from the omeka/archive/fullsize folder, I can then upload the reduced image files to the folder. I've done this with a couple of files, but haven't done them all yet. I wanted to ask if there are any unforeseen problems that might occur before I delete all my fullsize images and replace them with smaller ones.
As long as you're keeping the filenames exactly the same so Omeka can still find the images to display them, Omeka doesn't actually care (or know) at all what size the images are.