Fixing Album Art on iTunes

As I uploaded the Red Hot Chili Peppers CD By the Way and Nirvana's Nevermind to my iTunes library on my computer, I was given an awful surprise when I checked it's progress on my iPod. The library on my computer was not the same as the one on my iPod, so moving CD music from computer to iPod was difficult, but I was able to make it work, or so I thought. When I scrolled through my iPod to see if my RHCP songs had loaded, I saw that most of my album artwork was missing. Not having complete album art in my collection really bothers me, and I was getting very frustrated because I couldn't figure out why they weren't there. Then I realized that the only albums missing their pictures were ones that I had gotten off of CDs, and all the songs I purchased through iTunes still had their pictures.
Through the research I did, I couldn't figure out why it happened, but I found ways to fix the problem. I tried a few possible fixes, but none seemed to be working. I pieced together my own fix from the many sites I visited for answers.

First, I had to check a setting in iTunes that let me manually manage music.

After that, I tried right clicking the song and looked for the "Get album art" option, but this option wouldn't appear for the songs already on my iPod for some reason. Instead, I had to click the "Get Info" option after right clicking. Once on "Get Info", I had to manually add the artwork. For Sia's 1000 Forms of Fear, for example, I had to save an image of the album art to my computer, then while on "Get Info" click "add artwork" and choose the image I saved. This went down for each and every song that had missing album art. I figured out I could select several songs of the same album (and only of the same album)and do it at one time rather than putting the same image for each song individually. That saved a little time, but overall it took a long while and seemed unnecessary. Finally, after going through all my albums and double checking, the peace of my iPod was restored. For some reason, iTunes was unable to do it for me, even though the correct album art was with the correct albums before I plugged in my iPod. Now every time I plug in my iPod to the computer, I'm worried it will happen again. In fact, it did, but happened to ALL of my music. Fortunately, it fixed itself after a few minutes.
     I really hope this will come in handy for someone! I know this would have been useful to find in one post rather than searching the webs for information. Let me know if this helped in the comments below and ask me if there is anything else I could help you with!!