image link is the full URL starting with http or https to the product's main image. The image can be sourced from any server or website. It’s used to display an image in the feedback request email and feedback form. It is an optional filed in a sales file and a required field for a product catalogue. 
If you don’t wish to link to individual product images, the link can point to any suitable image of your choice, for example, your brand's logo.
Usage is as follows:
File typeTXT/CSV file field name
XML field name (case sensitive)
Required/Optional
Default value
Sales fileimage link
N/A
Optional
None
Product catalogueimage link
N/ARequired
None