Collaborative, media intensive long document

Question

I'm planning to create a long document (book) with a lot of images.

Usually I'd use some LaTeX flavour and git. However, there are two big disadvantages:

1. Co-worker can only handle "user friendly" applications (e.g., Word)
2. Many many images. git does not like huge binaries

Requirements:

• some kind of version control
• collaborative
• images
• "user friendly" (you know what I mean?)
• future proof (none of my potential successors could handle LaTeX/git)

My current plan is to ask the co-workers to send me their images and plain texts and then doing the formatting myself (using LaTeX/git)

This is not a professional project, I guess each contributor (2 -- 3 in total) will spend no more than 2h per week on the project.

I use linux, others use Windows. I have some webspace, if that's helpful.