If you or your students are adding multiple images per post, you should download the Contact Sheet plug-in (or similar image management plugin). There are a host of stylesheets that you can drop in to adjust the placement and shape of thumbnails. Contact Sheet with the default Charrette styling appears below. You can control the size of the thumbnails, medium sized image and large image (lightbox size) in the Settings>Media area. If you’ve already uploaded images, you can use the “Regenerate Thumbnails” tool to make more thumbnails.
If you are dropping in single images, insert images from the Add Media button or insert using HTML code.
Make an image the maximum width by using the classname “fullwidth” in an image tag.