When trying to recreate a signature from an existing signature, copy+pasting the signature information into Visual mode will disrupt the formatting and images, which is why you may be having trouble. 

What we recommend is the following:

1. In Settings > Signatures > click into the signature you'd like to copy from. 

2. Select Edit using HTML mode

3. Select and copy the HTML code from the text box. Then, close out of that signature. When prompted, select Discard changes. 

4. Go back to Signatures > Add a signature > Edit using HTML Mode > Delete the code in the box > Paste the code from your other signature. 

5. Hit Create. 

6. From there, the signature will have converted to Visual mode. You can edit it as needed, then save the edited version.