Yes, you can! However, we don't recommend using images in your sequences, as the main purpose of most cold emails and follow-ups is to look like they're 100% handwritten. When you send regular emails, you usually don't include images. You just send your customer an email with a human message.
To add an image, simply select the Insert/edit image or Upload image option at the bottom of your email template:
P.S. Try to avoid using images with spaces in the name. Some email clients make auto-replacing "-" to "+" and it can break the link.