Beyond the photos of a gallery, you can create dedicated products.
Key points 
Enter title, description, price (excl. tax), image
A product is a draft by default, to be published to make it visible
For digital: automatic or manual delivery
Create a productIn the store, add a product by entering its type (digital or physical), its title, its description, its price (excluding tax) and an image. As long as it is a draft, it is not visible; publish it to put it on sale.
Digital delivery methodFor a digital product, choose the delivery:
Automatic: the client receives their download link immediately after payment
Manual: you send the files yourself after processing
Is the price excl. or incl. tax? You enter a price excluding tax; VAT applies according to your scheme.
My product doesn't appear? Check that it is published (and not a draft).
Difference between a product and selling the photos of a gallery? Products are standalone items; gallery sales concern the photos imported into that gallery.
Vendre les photos d'une galerie
Activer la vente sur une galerie, fixer les prix, offrir des photos et vendre des dossiers entiers.