Export 500 different images using our PSD

We are a greetings card company and have a PSD we use to create nice product images.

We will provide this PSD along with 500 designs for you to use - we then use https://unsplash.com/ for our flatlay background images. What we need is for some one to:

1. Open PSD and then open the PSB layer
2. Paste 1 of the 500 designs we will provide
3. Save PSB and switch back to the PSD parent
4. Use Unsplash to find a relavent background image (we don't mind using flat colour for some, but most we'd like a flat photo background like the examples we've included)
5. Save as a JPG

Here's a video showing you what the PSD looks like, and how easy it is to change the PSB and switch/paste backgrounds in: https://streamable.com/9mslvw

The end result will be 500 JPGs of greetings cards with various background - ideally no more than 5-7 using the same background