1: sometimes Jpeg is broken, I have those with photography, when there is 80% of the image, and the rest of some stripes and gray squares.

2: gray stripes and squares, obtained from the uncopied file or not proven or imprinted incorrectly.
They cannot ruin themselves.

1: Hm, strange, and I thought if the files lie on the computer for a long time and they can not be copied anywhere, then they can get damaged, so I copy files from time to time from one folder to another.