To get started adding images to your email templates you can head to the Bulk Email page, this is found by going to the Marketing tab » Email » Bulk Email.
From here you can create a new template or edit an existing template (click Start from a Template at the top and choose a template to work with).
To add an image to your template simply click anywhere on the template that you are creating that you would like an image to be placed, then click the Insert/Edit Image button.
Next, click the Upload link to upload your image or click the Upload Icon to choose an image you previously uploaded. You can upload images right from your computer, you no longer need to have these images hosted somewhere else on the internet.
Once the image is uploaded and added to your template you can click on the image within the template to make edits such as cropping, rotating, resizing and brightness and contrast changes.
You can also view our article on How do I create an email template? if you need further help.