This does not work in Endeavour anymore so please advise the client we are no longer able to offer this facility and suggest they use this free service: Postimages — free image hosting / image upload
After downloading the image that the client sent go to Endeavour, click on the Files module on the menu and click on File Upload.
Add the File the user has provided us with on the green +Add File on the top right-hand side.
You should get this box where you can drop the file or upload it.
Upload the file, click Save and you will get the link you are going to use to add the image to the user's signature.