It seems like Imgur was profitable from Day 1, but the early days were profitable through donations!
https://www.neowin.net/news/from-rags-to-riches-the-story-of...
Quote: "Imgur has always been profitable right from the very beginning and the only time I ever had to spend money on it was for the initial domain name because as soon as I released it, people liked it so much that they were donating and so Imgur survived for the first six months just purely on donations."