Decoding: The numbers to the left of the grid below are an encoding of the image. Each row of numbers tells you how to fill in a row of pixels in the grid from left to right. The first number tells how many blanks there are, then the second tells you how many colored squares follow the blanks, then the next number tells you how many blanks follow the squares, and on and on, until there are no more numbers in the row. Complete all the rows in this way, and you'll have a picture!
Encoding: You can make your own puzzles by drawing a picture in a grid, and then writing the code numbers for each row. Practice doing that on this picture (which is supposed to look like a heart).