Instagram is one of the most difficult apps for developers to schedule auto posting without using API. Instagram is specifically designed to support uploads from mobile phones only. Instagram team only gives whitelist access to limited third-party apps for automatic posting on a case by case basis. Another reason is Instagram team want to fight spam and low quality photos.
I was looking for a way to auto posting from website to Instagram page using PHP/cURL without using API since last two years. Lately I found two websites that are discussing about this topic.
Initially I was not able to make the coding working immediately after download the source files due to several issues such as PHP 5.5 vs 5.6 issue as well as new signature key from instagram app. In this tutorial, I will show you a working draft to auto post single photo to Instagram page using PHP/cURL. I am take no responsibility if your account banned by Instagram. :)