New answers tagged graphics
Try disabling either the GPU or the integrated graphics card driver: http://blog.b-nm.at/2015/08/03/macbook-pro-gpu-problems-gpureset-freezing/
Your MacBook Air has integrated graphics so the system memory (total RAM) is shared between the OS (traditional RAM) and integrated graphics (stuff that handles drawing pictures on the CPU, that needs some RAM to itself as well). OS X dynamically partitions that amount of VRAM versus system RAM at any given time (per Apple). Windows likely doesn't have this ...
Let me guess: the issue appeared with the 10.10.3 update? Well, then I am 98% certain it is a bug in OS X Yosemite. Your issue is related with this one. Users report erratic kernel panics and some users have graphics glitches like you. The only common feature is having a Intel HD 4000 GPU. On MacBook Pros with dual GPU you can avoid the problem by ...
I think the data comes from CDDB, or at least it used to, back in the day. You can edit (only add?) album art in iTunes by dragging image files onto the album art display. I don't know of any way to do it with only iOS.
There's no mechanism in iOS for modifying album artwork associated with your music. You'll need to use iTunes on Mac OS X or Windows. From there, you can manually choose your artwork, or ask iTunes to search for appropriate artwork.
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