Can I email pictures to Walmart to get them developed?

It depends upon the Walmart in your area. Some stores offer/ed this service. Some are converting to a new system. It’s worth checking with the local stores in order to find out what they currently offer and how how they can meet your needs.

Email, no. Upload, yes. Same with Walgreens and CVS.

Like, per picture? Like if I wanted 4 pictures I’d just pay for 4?

You mean printed? You ca upload to Snapfish and get them printed same day at Walgreens.

How much per picture? I picked up this cool picture box at Goodwill today. You can put pictures on all four sides and the top. Plus, inside, are some racks inside with room for 80 more pictures! I don’t know who I’d show them all to, except myself, but I’d like to pick my best pics to print for this project.