How to stop iTunes on my PC to upload random picture on my iTunes iPhone?

I download a lot of music from my PC iTunes to my iPhone iTunes. On the PC you have the option to choose the "Artwork" of each song you have on there, which I always personally choose, to fit with the song and/or artist you know, but once I drag them to my iPhone, on my iPhone in iTunes the songs are there, but with random pictures that I used in the past. How do I change that to make sure the pictures I chose on my laptop, stay while going on my iPhone?