Open the „Settings“ for the open call for which you wish to create a discount code. You get there via the "Settings" button next to the call title on hosts.picter.com.
Under Basic Info:
Upload a cover image in JPG and 4:3 aspect ratio (2000x1500px)
If you want to replace an existing image use the "trash can symbol" to remove the old file before uploading the new file.
Confirm the changes via "Save"
Optional: Provide a caption for the cover image