on your computer desktop? You can use a image resizer
https://imageresizer.com/

in css?

body {
  background: url('https://24wallpapers.com/wallpapers/Blue-background');
  background-size: 50px 60px; /* wxh */
}

solution

Here's how. You can resize your background image, or wallpaper, by using some css.

body {
  background-size: 100px 100px;
}

That just makes the height and width 100px. You can also make the image fit in.

body {
  object-fit: cover;
}

So that makes it fit. Just use that for your images. Btw, it doesn't have to be body. You need to put an id, to your image, and call a # at the beginning when you put something instead of body.
That should work

Do you want to crop it or resize it? There are various offline programs that can edit photos, as well as online image editors that allow you to crop and resize.