I think someone in the revenue delta does not understand the stock business. You are not the seller of the image to the end user and there for no sales tax would be collected.

You are not selling the image (tangible) but a license to use it (intangible). I think that isn't covered by Sales Tax even if the sale occurred in Washington State. I think the employee misunderstood.

And the sort answer is that you cannot know where your images were licensed, so even if the intangible license were covered, you can't separate out locations.

In some states they have reciepts tax which have to be paid either by the store or can be passed on to the client.From hat I can see you are in a state that has a sales tax. I would ask to speak to a supervisor and tell them your situation