Photographers can protect their images when posting online by using watermarks and including a copyright notice which is the copyright symbol, their name and date the image was created e.g. © John Smith 2020, indicating that the image is copyrighted and they are the copyright owner.    Additionally before supplying hi-images to clients, they should provide an image licensing agreement outlining the terms under which the usage rights have been granted together with a schedule list and thumbnails of the image(s) licensed.  Included in the metadata of the licensed image(s), in the Rights Usage Terms box, should be the licensing terms, the name of the licensee, and when the licence expires.  Invoices should include terms and conditions of supply on the rear or as a separate attachment when sending by email.  The terms can state specifically that hi-res images supplied should be deleted after a period of time or alternatively, permission for the client to retain the image on file for any possible future use; bank details for payment and payment terms; specifying in bold lettering that non-payment of the invoice (after 30 days for example) will revoke the licence or that the licence will only take effect on receipt of payment of the invoice.