Who uses the Instagram you know that there is no other way to post photos on it than through your official app and this has been true since before it was bought by Facebook. There is an API for third party developers and it is quite complete, but it does not offer the upload option.
The app Grids for Mac, from ThinkTime Creations, explores everything possible through the API.
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With Grids, users have a nice interface, optimized for Retina screens and designed with OS X Yosemite, perfect to accompany their users. feeds Instagram. It allows you to adjust the size of the images, spacing and background color, so that the look is the way you prefer.
In addition to viewing photos / videos posted by people who follow, Grids users can like and comment, follow and search for new people, browse by tags, favor different things, receive notifications, among others.
If you're a regular Instagram user, be sure to check out Grids.