Submitting a captioned image to Pictory doesn’t affect your copyright on it: you retain your copyright to your work. By submitting work, you allow Pictory to publish your work online on the Pictory showcase blog or in a navigation element on the site. I’ll reach out directly with an invitation for anything beyond that (such as gallery events, books, other promotions).
Don’t upload anything that isn’t your own original work. If you didn’t shoot the photo or work on the caption, it’s not right for Pictory.