Hand-coloring of photographs is when someone takes a black and white photo and adds color to it using some special tools like paintbrushes, pencils etc.
It's like when you color on your coloring book with your crayons, but instead of the coloring book, you're coloring on a picture of your grandma's wedding.
First, the person who colored the photo has to decide what colors they want to use for each part of the photo. For example, they might use green for the grass and trees, blue for the sky, and red for the roses in the wedding bouquet.
Then they have to be very careful and use a steady hand as they color in each part of the photo. They might use a small brush to add color to the flowers, and a bigger brush to add color to the sky.
It can take a long time to hand-color a photograph, but when it's done, it can be really beautiful and look like a real-life picture.
Hand-coloring used to be very popular before color photography was invented, because it was the only way to make a black and white photo look like it was in color. Nowadays, it's become a bit of a lost art, but some people still hand-color photos as a hobby or as part of their work in the art industry.