Clothing and Covering the Aurah

Q: Is wearing a skull cap mandatory whilst praying Salaah?

Q: Can we perform salaah with clothes on which has animals like Puma shirts, etc.?

Q: I wear a trousers belt, it's leather. I don't know what kind of animal skin was used to make this leather belt. I heard that if you wear leather made with pig skin and if you pray salah with it, it wouldn't be accepted, it's nearly impossible to tell if the leather is pig skin or not because where you buy it, it doesn't says. Would my salah be valid? 

Q: Can we wear a leather belt in namaaz or not?

Q: Zaid has a towel ihraam which is made in such a way that there are very small holes in the ihraam cloth. When wearing the ihraam, little skin is visible from the holes. Zaid prayed salaah, did his umrah and Hajj with the above mentioned ihraam on. According to Shariah is his salaah, umrah and Hajj valid? If it isn't valid, what should be done to compensate?

Q:

1. If one prayed salaah while wearing clothes with a human picture which one missed to see and saw only after looking at them carefully, would those salaahss be valid? Does one need to repeat those salaahs?

2. What about praying salaah in clothes which have clear human/animal pictures?

3. If one prays next to or in front or behind someone wearing such clothes or wearing a work ID with visible picture of the person (around 2 inches in lenth and 2 inches in width) would the salaah be valid due to being in close proximity of a picture?

Q: “Quarter of the head is approximately the amount of the palm with the fingers.” So to estimate this, do I place my hand vertically on my head or horizontally?

What if some of my hair is showing and some of my awrah from my arm is showing? Do I need to add them up together? 

Q: I’ve noticed that in fard wudu, only a quarter of your head needs to me washed. And when awrah is shown during salah, then only if it is under a quarter, the salah is deemed valid.

Today a little strand of my hair was showing during salah. I’d like to know how to measure a quarter of my head.

Q: If a woman performs salah with 3/4 length trousers and then tights under them, wherein no part of her leg is visible, is her salah valid?

Q: During salaah, I sometimes wear a shirt which has a low collar, so a bit of my upper chest (under the bone below the neck) neck gets visible. Is the salaah valid?

Also, how much portion of the chest should be covered by men during salaah?