Welcome to YT. He is a little cutie and yes, the terrier is a different sort of dog to train. You kind of have to work with their stubborn streak and not against it since trying to fight it just incites their terrier disposition.
Can't help you with the photo. I am the worst dealing with that sort of thing.
He is just now at the age (usually at 16 weeks of age)that he can start to control his output of urine. Up until that age they have very little control so it can be a lot of stress on you at first when trying to train a pup. It's kind of like expecting a new born to not potty in it's diaper. Sometimes they do learn some bad habits during those first weeks in your home when they can't control their pottying. The accidents can set up scent in the home that encourage them to continue to potty in those places. You can't smell them but the pup can even after you clean the area as well as you know how.
Hopefully you will get through this but it takes time. Try giving him a healthy treat when he gets it right rather than punishing when he gets it wrong. Scolding can cause him to sneak off and potty where you can't see him. They really respond better to reward than the punishment cycle.