So you want each image in the gallery to be a separate product in PowerStore?
for this you would need to add each separate image as a product in PowerStore
Then, product by product, go to the detail page and make note of the ProductID querystring variable for that product, for example:
Then in power gallery add a link to the product detail page in the image details passing the ProductID value:
<a href="products_detail.php?ProductID=14">Purchase this image</a>