I've figured out how to use the thumbnail size and medium size pictures that are created for photos in our galleries, in blog posts instead of the full size images.

Use the Insert Image link at the bottom of the post entry window, to add the full size version of your image to the post and then edit the filename as follows to get the size image you want to use.

The thumbnail images have _thumb appended to the name of the file before the .jpg extension.

so, blackbird1.jpg becomes blackbird1_thumb.jpg

To use the images that are displayed in your gallery when you click on a thumbnail, use the name of the file with "_medium" between the name of the image and .jpg

so blackbird1.jpg becomes blackbird1_medium.jpg

This means I can upload fairly large pictures to my gallery so people can see my pictures in detail, and use them in blog posts as well without having to upload special sizes, that will fit in the blog window.