[Update]: This post was updated on December 10, 2019.

Old versions of Office 365 OWA email signature editor didn’t have a built-in functionality like a button or easily accessible HTML source for adding images to email signatures. Luckily, it was very easy to overcome that limitation. Here is what you needed to do:

1. Upload your image to a web location (I used the one located here).
2. Open the web location, right-click the image and select Copy or any similar option in your browser (for example, Copy image in Firefox and Chrome, or Copy image to clipboard in Opera).
   
   Note: It’s important that you copy the image and not only its URL.
   
3. Open the Office 365 OWA email signature editor, navigate to the part where you want to insert the image and press Ctrl+V on your keyboard.
   With the new versions of Outlook on the web, you can just click the image icon in the signature editor to insert the image from your computer:
   
4. If your signature looks as expected, click the Save button on the top of the settings window.
5. Now, open a new message to verify your Office 365 email signature.
   
   Note: When creating the email signature, you can enable the Automatically include my signature on new messages that I compose option to always automatically add signatures to new messages.
   
   Or you can manually insert the signature using the Insert signature button in the message editor if you leave the above option unchecked.
   
6. Before you start sending out emails, make sure to test if your signature works correctly.

Hyperlink your signature image

To add a hyperlink to the image in your email signature, left-click on the image and when it is highlighted/selected, click the Insert hyperlink icon and provide a hyperlink URL.

Linked images

When you apply the above solution, what you effectively get is a so called ‘linked image’. The problem with linked images is that they tend to get blocked by popular email clients. Go to the Images in email signatures – linked or embedded? article to learn more about the pros and cons of using them.

To globally add email signatures for Office 365 users, you don’t have to learn how to manage Office 365 transport rules. CodeTwo Email Signatures 365 is an easy to use alternative. Benefits include:

• easy email signature template design thanks to built-in WYSIWYG email signature template editor;
• no HTML skills needed;
• images and dynamic placeholders added with a few mouse-clicks;
• users can see their signatures when writing emails;
• non-IT staff can manage email signatures without access to Office 365 Admin Panel;
• consistent email signatures on all email clients and mobile devices.

See also:

• How to set up or change email signature in Outlook on the Web
• Problems with email signatures in Office 365
• How to create company-wide email signatures and disclaimers in Office 365