I have Sony Xperia phone which has a physical dedicated camera button, that doubles as a shutter button once camera is activated. Despite of that, no matter how much I tried I failed to take a legible picture of back of my neck (I needed it to be sharp so I could send it to my doctor) and after many tries (even with using a mirror) I gave up and had someone to do it for me.

It is really hard to take a sharp picture of something close without looking, especially with low light conditions.