No data to back it up, but I've always heard under 10 feet feet breaks bones, over 10 feet kills.
Personally, I wouldn't want to fall (or jump) more than 4 or 5 feet. I used to jump out of a 8 foot hay loft when I was a teenager, but I'm more brittle and almost twice the weight now. Bigger thud.
Most new ladders have angle diagrams on the side to help ensure the proper angle. One simple check is to put the tips of your shoes against the bottom of the ladder, and reach straight out to a rung. You should be able to grasp the rung without bending or stretching, and without bending your elbows. It's not exact, but it should get you close.
Just going from your photo, that ladder looks a bit too steep to me. It might just be the camera perspective, but the treads don't look parallel to the ground. It just "looks" steep to me, too easy to fall backward or slide sideways.
I spend a lot of time on ladders (I've got 5 or 6 ladders of various sizes), including my 24' fiberglass extension ladder. Maybe I've just been lucky, but I've never had an accident (or close call) that involved a ladder. If you take precautions setting them up, and pay attention they are generally safe. Don't lean out, always stand upright keeping your center of gravity on the ladder. If you can't reach, climb down and move the ladder. Never stand on the top rung, you could lose your balance. If you're climbing up on the roof, make sure the ladder extends a few feet above the roof edge. You should be able to hold the ladder in your hand and step sideways from the roof back to the ladder without leaning.