Give me API details for instagram and pinterest and I will set up an application in the langauge of your choice that will allow you to select a large collection of images, adjust their details and submit them to the two websites.
If I do run into the problem of them not being able to handle the request, I will look at multi access or threading to increase speed.
If it still is a problem, I could do simulated web posts (as long as they don't have captcha)