I'm trying to work out how the internet business model might differ from the more brick and mortar model in a couple of aspects.

My ultimate question is probably too convoluted for a first post so let me start with

Definition: A POD means print on demand company - typically where there are various account holders. The account holders upload images. The images are then displayed on products and offered for sale. The customer pays the POD, not the account holder. The POD takes the orders, applies the image to the product and ships it out. The account holder gets a cut of the sale.

Let's set aside, for this purpose, copyright registration in the USA.

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Part A - the initial reaction I got when I described this scenario was one infringement. But that doesn't sound right. That reaction was based on the idea that if a factory takes an image and prints 10,000 posters, that is just one infringement. In this scenario it is the one "factory" printing the same artwork, but different sources.

Let me reset this scene:
Larry, Curly and Mo do not know one another. They are not working together. All three have accounts to upload images to sell products on the POD Teexxxx.com.

They each scour the internet on Feb 25 2018, looking specifically for designs to steal.
They don't actually know what designs they are stealing. They use a search script directed at other POD sites to find images. They don't look at them, just upload the image files together with the stolen title and description.

In this scenario the searches by Larry, Curly and Mo happen to include the same design. Larry and Mo found the image on Redxxxxxx. Mo found the image on Spreadxxxxx.

They upload the images to the site and the site creates mockups to offer the design for sale on products.

The page attributable to Larry sold 50 product, Curly sold nothing, Mo sold 5.
Who is liable for infringement, and how many infringements are there?

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I hope I did a credible job with the above.
Thanks for your time and thoughts.