Create a Signature and Insert an Image
After signing into your account, follow these steps to create a signature in Outlook for Mac and insert an image into it.
Click Outlook > Preferences. Under Email, click Signatures. Click Add a signature (the plus icon). Enter text for your signature, using the formatting tools (font size and color, highlighting, etc. ) to create the appearance you want. Place the cursor where you would like to insert your image, and click Pictures in the ribbon menu. Select Photo Browser if you want to pick a photo from the Photos app, or Picture from File to navigate to an image from your computer. Select the image you want to add, and click Insert. Resize your image if necessary by clicking and dragging the image handles. Enter a name for your signature in the Signature Name field. Click Save icon at the top of the signature window. Close the signature editing window after saving. Your new signature will now be available in the list of signatures.
Select Photo Browser if you want to pick a photo from the Photos app, or Picture from File to navigate to an image from your computer.