I take friendships/relationships very seriously. To be my friend there are certain traits one must have (which are written in my Bible and taught by Dr. Charles Stanley), and of course I don't ask anything more of another that I myself wouldn't bring into a friendship/relationship. I always like to give people a chance, even though I have been burnt so many times and I have trust issues big time, one needs time in order to truly get to know someone. But if just one of those traits are missing then I cannot consider them a friend. It is not being mean, but only using safe guidelines to protect myself and to have healthy relationships with others. If you let every Tom, Dick and Harry be your friend no matter how they act, their character, etc. you run the risk of getting seriously hurt or influenced down the wrong path. No one needs toxic relationships in their lives and God doesn't want us to either.
When it comes to social networks I have always had a lot of problems, especially with Facebook. Too many people on there don't really want to "be friends" it is just a popularity contest to see how many friends one can collect. Friendship is a two way street not all one way or one person always doing the reaching out and communicating. If it is not equally two way open communication then it is by no means a friendship. I have had people want to be my friend and I accept in order to get to know them better, write them and thank them for their friendship request and then never to hear from them ever again...those are the first ones I let go after giving a lengthy time for them to make an effort to be friends. When they show no signs of being a friend, they are the first to go and I give no warnings.
I have let some go that I have given fair warning to due to their language and poor choice of words. As a Christian, one should expect other Christians to talk with a clean mouth and not have a potty mouth (using curse words). I always let them know in a loving way that when they use such words they ruin their testimony for Christ and that I really don't want to open my profile page and see those kinds of things on the news feeds. If it continues, I let them go. I still love them, but I don't need to put up with that and God doesn't want us to either. I feel by allowing people like that on as my friend, what does that say about me and my testimony of Christ. Other Christians could check out my profile page and start clicking on my friends to see what type of people I allow in my life, (I do that when someone sends me a friends request, I check them out), and if they see posts of friends using bad language or posting pictures of half naked people, that is not good. It speaks volumes about my character and my testimony.
So no, there is nothing wrong with un-friending someone and not telling them. 9 out of 10 times guaranteed since they never treated you much as a friend in the first place, they probably didn't even notice that you un-friended them. I also do not think it is right for anyone to post pictures of another when they know how that person feels about their picture being taken, especially if it is an unflattering pic. If they want to post it because of something else going on in the pic that they want to share, then they could have easily cropped you out of it when they knew you didn't want it posted.
Friendships/relationships are a valuable precious thing and need to be treated as such. When someone truly cares and loves someone, their actions will show it. The old saying is true...."Actions speak louder than words"!
When it comes to friends, who needs 100 or more anyway, they are not real or true friends. All one needs is one or two or three really good, close, true friends, and you are the richest person in the world.
God bless and take care.