In the WYSIWG editor, when you have highlighted an image by clicking on it, you will see an "Insert/Edit Image" button in the bottom button bar. With an image highlighted, this will give you access to the properties box for that image, and allow you to manipulate most of the relevant HTML properties of the image.
You can manipulate any of the following image properties:
- Image dimensions
- Text wrapping around image
- Border size, style, and color
- Alternate text to be displayed when the image is not displayed
Many of these are valuable editing properties, but the alternate text is worth paying attention to. Many, if not most, of today's email inboxes do not display images automatically. When the email first appears, only a placeholder for the image will be shown. Although the best idea is to ensure that your email design is not entirely dependant on images, if images are unavoidable, it can be useful to include alternate text that will show up in the mouse-over of many email clients.