These artworks are made from what are called either "fuse beads" or "iron beads," from companies like Perler in America, Hama in the UK, and Nabbi from Sweden. All three claim to be the "original" fuse beads, but I believe Nabbi are actually the first. I use all three for their various color gradations. It is a very fun hobby. It is time consuming and meticulous, but not tedious because it is fun.
Marle and Crono from Chrono Trigger
Bomberman from Super Bomberman 5 on the SNES/SFC
The twin ships from Galaga
Guzuta, Pinky, Akabei, and Aosuke!
Dig Dug
Arkanoid II: Revenge of Doh
Shin from Area 88, my favorite shmup on the Super Famicom
Etna from Disgaea
A larger-scale Bomberman
Arle and Carbunkle from Puyo Puyo 2, plus a Space Invader up in the corner.
Marth and Sheeda from Fire Emblem on the Super Famicom.
The following three are from the SNK Gals Fighters game on the Neo Geo Pocket Color:
Athena
Yuri
Mai
Hikaru, Max, and Millia from Macross: Scrambled Valkyrie on the Super Famicom. These are big and took a lot of time to make!