About Using images preview

I need an information about

I’d like to build an on line service for ready graphics, in particular for print graphics and not web site.
People that can’t edit a graphic template with a graphic designer or that don’t have an Adobe software, can choose on my website one of the Envato print templates, insert their content in a form, and choose the number of prints to receive at home.

So, my work is to insert their content in the chosen theme and send the ready to print pdf to the printer service.
I have a recharge on this service.
To show items, I would use the preview images of the authors in my website.

Do you think is it possibile? Can I download from graphicRiver and re-upload on my website the item images?

I also offer for each item the affiliation direct link to GraphicRiver.