Mac wallpaper

Good evening,

Apple menu/System Preferences/Desktop & Screen Saver/Desktop tab, your photo must be in your user images folder, which you select along with your image, where you can see the presence of your choice and, normally, no problem.

Explain what you did.

From Finder, menu Help/Mac Help/change wallpaper, it should be explained.

Changing the Desktop Background

The background of your screen is part of the desktop (where you work with icons, windows, and applications). You can change the desktop background by applying one of the patterns, colors, or images provided with Mac OS X, but you can also choose to display your own image.

Choose Apple menu > System Preferences and click on Desktop & Screen Saver.
Click on Desktop, then select a collection of images from the list on the left.
Several collections come with Mac OS X. You can also search for images in your Images folder or select Choose Folder to locate an image at another location.

Right-click on an image you want to use as your desktop wallpaper.
To have the desktop image change at regular intervals or at a specific time, check the "Change image" box, then choose a time from the drop-down menu. This may reduce the performance of applications using a lot of graphics, such as games.

You can also change the background by holding the Control key, then clicking on the desktop and selecting Change Desktop Background from the shortcut menu.

If your images do not appear, you may need to save them in another format (JPEG, TIFF, or PICT, for example) using an application like Preview (in your Applications folder).
When it's urgent, it's already too late (Talleyrand)

It's still not working! I can change the wallpaper... when I restart, sometimes the wallpaper doesn't change, but when I turn it off and back on, it puts the beach wallpaper back.
Yet I'm doing the right steps, I've put my image in finder/images. Then Apple menu/system preferences/Desktop & Screen Saver/Desktop tab, then I open my folder with the +, I choose my image and it works.
My image is in jpg format.

create a wallpapers folder, with your wallpapers inside
click on apple
system preferences
in the left menu, click on the small + at the bottom
add your wallpapers folder
select your wallpaper
and normally after a restart, it will still be the same