Rogaine / regaine help please. How do I know if it has lost effectiveness?

Ok so i have been using Rogaine (Regaine in UK) for best part of 7 years now. I didn't have a lot of hair loss but enough on the crown for people to notice. I'm nearly 34 years old.

So the first 8 months it worked wonders to the point where people couldn't even see my scalp any more. But after about 12 months I noticed hair very gradually starting to thin again on the crown and slowly but surely over the years hairs have continued to fall out up until 2 years ago since when the shed has stabilised and not much more has come out. However i now have a bald patch on the crown which slightly has made its way to the front but not much. The hairs on the crown I like thin , dead tangy type hairs of no use.

So the question ...has Rogaine for me lost its effectiveness .. I continue to use it and spend money every month on it .. am I just wasting money? And very importantly and my main concern - how do I know that the hair I do have is there because of Rogaine? Because if it isn't than well I should stop using. I've attached a pic of my crown in case it is of any use to experts.

I would really like it if some experts in the field would answer this for me as it has been bugging me for a few years now.