ITMI appears to be 100% legitimate, since there are many references to them in articles at reputable sites. They help their graduates with career placement. Their training costs about 3000USD. Heres a link to their website:
http://www.itmitourtraining.com/
An article at JobMonkey says tour guides/directors start out at 15-18USD per hour, and experienced tour guides make 20-25USD per hour with time and a half for overtime. The earning can be even higher if you work for a major company. Is the 3000USD worth it? I'd say so, if it gets you the career you love.
Is the cost ot the ITMI course too much right now? Cherie Anderson offers a six-week course called "Get Paid To Travel" for 120USD that covers the basics; you can read about it and enroll here:
ed2go online courses
This course can either be taken online through the above site, or through an accredited college or university if there's one offering it in your area (there's a form for locating a school near you at the site).
Vasily