Great hack from Mailjet haha. This is helpful, I design a ton of email.

I took a look at the site.

One thing I noticed in terms of the Advertising page is that you don't provide any traffic numbers which are usually important for any advertisers that's willing to spend $. They need to understand the CAC.

In terms of users, it seems it has the same problem as twitter in which most of the people visiting the product are observers vs. contributors. I think that's an overall problem for user-generated content but in this case it's even harder since it's only the captions and not the actual images that are generated by the user. There has to be some sort of underlying benefit for users but so far it's simply entertainment. The great thing about WIP is the fact that people actually follow their todo's from the platform and can share knowledge and gather feedback for their products. Perhaps, you need to find that same underlying factor that pulls people in.

I think your suggestion of letting users add their own photos make sense and a potential good start. Think about it from the imgur or instagram perspective, people add pictures to share their experiences, or to get that short term gratification of likes, etc. Perhaps something like that could help increase engagement? But then again not sure what your goal is with the platform.

Hope this helps. I'll keep thinking about other ideas!