Comment on Promote Clickbank Affiliate Products by SEO Dave.
Personally I always upload to my own website so the image is always the image I expect it to be and if the affiliate deletes the image your copy is safe on your websites server.
If you don’t want to mess around with uploading images using FTP create a new Static Page (“Pages” >> “Add New”), call it something like “Temp Images” and set to “Visibility : Private” (this will stop anyone seeing it on your blog if you accidentally publish it).
Working in Text mode (so you can seete HTML code of images) use the “Add Media” button to upload images to that private page, but save it as draft (never publish it). When you upload an image to WordPress you’ll get a URL like: https://stallion-theme.co.uk/wp-content/uploads/stallion-300-250.gif
You can use that type of image URL for your banner images, just copy and paste it into a custom ad widget for example, sort of hotlinking to your own website.