Company logos and images can be added your Newsletter Template to be included in each Edition of your Newsletter.
Add a logo to your Newsletter
Select a Newsletter
Click Newsletter Settings & Template
In the Email header section, click the image icon
Select and insert the image of your choice
Resize the image if needed
Click Save
If you're including a logo in the header or footer, be aware that the full width of the email is about 600px. To achieve the best appearance and resolution, a good size guideline for a full width image in the header or footer would be a width in the 600px to 1000px range.