Ask HN: How "illegal" is the application I am building?

I am currently building an iPhone app that links popular fashion on Instagram with retailers and stores.

Content "creation" is done manually by checking Instagram's popular feed (using the Instagram API) and copy/pasting popular images of fashion items into a database (including the stores links where you can buy them).

Obviously I'm worried about copyright issues. I'm not storing any images (only the links), but I don't think that makes any difference. My app credits the respective Instagram user as the owner of the picture - but again, I don't think that makes any difference. Is this "fair use" of the data, and if not - what's the point for Instagram having an API? Can anyone spare some legal knowledge?