there is a way to 'trick' instagram into thinking you're accessing the site via an iPhone, which does allow for photo uploads. first off, open safari and head to preferences > advanced and make sure show develop menu in menu bar is toggled on. from there, head to the instagram website and log in to your account. then select develop > user agent > safari - iOS 10 - iPhone. instagram website should automatically reload (manually refresh if not) and display the mobile version of the site, complete with upload functionality. select the camera icon, browse for the image you'd like to post and select choose. or use Flume/Uplet