I've been following this great thread since you kicked it off. With your latest pic the red pillar box put me somewhere in the uk but not conclusively. The yellow no parking lines
on the road also added weight that it was in the UK. Couldn't pick out the flag.
Certainly the building is very distinctive and I figured it as a famous institution of some sort. After a couple of searches without leads, I googled "famous yacht clubs UK" and up popped a picture of the Royal Yacht Squadron.
i've not been to the Isle of Wight but I did do some sailing at Lymington last year which is perhaps only about 40 miles or so from Cowes.
Now for the tricky bit - posting my own pic.