iTunes - Artists - images

In my itunes, i have no images stored against artists or albums as they take up unneccesary space when synced with iphone - however, since IOS 7 upgrade (??)) when i go into music on my phone, quite a few artists have images against them - where have they come from and is this a problem for space/capacity

It's usually normal for iTunes to pull in those images when songs are added to the library and there's no reason not to do it. The amount of space they take up is VERY negligle since they have low resolution and small dimensions. It'd take you probably at least 30 or more images to amount to a single MB of space usage. Assuming that a good quality AAC/MP3 file is usually in the 4-6MB range, that's like 150 album arts for the size of 1 music file..you get the math..don't sweat it..