I was really excited for this, but it is just a wrapper for the Google Art project. I am not really sure how you got the rights to be able to sell prints of these, or why you want to charge $9.99 a month for a pro version, but good luck!
One of your recently featured artworks (https://www.artpip.com/artwork/57a4cf0970f12152abacdf78) seems to be owned by the Van Gogh Museum and needs a license to be printed. If I wanted to order a print of that, do you have the correct license?
See [1] for an example of wikimedia's position on licencing:
'The official position taken by the Wikimedia Foundation is that "faithful reproductions of two-dimensional public domain works of art are public domain".'
Also, it's a $9.99 one-off payment, not monthly. Serving tens of thousands of high-res images a day adds up, so there's some extra paid features there for those that particularly enjoy the app and feel like supporting the project.
[1] https://commons.m.wikimedia.org/wiki/File:Van_Gogh_-_Starry_...
I can imagine a situation where an artwork is copyrighted but someone takes a photo of it and uploads it to Wikimedia saying 'here, use my photo'.. but they don't have rights over the original. Which would be like camming a film in the cinema and saying 'the original is copyrighted but my reproduction is PD'.
Not trying to knock the idea - I'm an artist myself and think anything that helps spread and communicate art is great - good on you. Just something to keep an eye on.
I've seen countless scummy stock photo sites selling NASA imagery for ridiculous prices (think $200 per image) when it's all completely free in the first place.