When creating an email template, there are several ways to include an image in your email. For the fundamentals on email templates, you may always view our article here: Creating Email Templates on that topic.
For image size, we recommend keeping that to 100-500 KB for best functionality.
If that image has been saved and hosted, you may paste that URL within the web address portion after selecting the 'insert image' button as shown below:
You may also paste in images to the body of a template. For pasted images, we recommend doing this one at a time if you do have multiple images. Additionally, you may need to 'sanitize' that image by copying it from Microsoft Word or your email prior to pasting into Crelate. This will also give you the capability to resize that image prior to pasting into your template.