How can you add the source if the image is not in the folder, or in another site?
I think I have seen a plug-in for adding Signature in the Store. Not sure.
Anyway, you may take a look.

P.S. Sorry, the store item I meant is for Forum Signature.

You have to search in the site language strings and add your custom content over there.

Search for strings "email"

Anastasiaa G,

upload you image in admin panel>>appearence>>edit theme>>graphics.

Add <img src="http://fullpathto_uploaded_image_here" alt="COOL TEXT here"> code to the needed email in admin panel>>languages>>find needed email text.

Example:

1. I have uploaded image to yoursitename.com/admin/theme/graphics
2. I have edited the email template in admin panel>>languages  to include my image

3. I have tested and I can see the image in my email

do you do this where it says edit theme...I do not know how.  do you copy it below into the edit css in its entirity...

David,
See image attached.

1. You are right. It is under "Edit theme".
2. Upload the image under "Graphics" tab
3. Copy URL of the uploaded image.
4. Go to admin panel>>languages
5.  Find needed phrase. And add <img src="http://paste copied image URL from step#3 here" alt="COOL TEXT here"> to the found phrase.  Don't forget to click "Save" once you are done editing the phrase.

It works for me! Great! Thank you so much!

You are welcome.