It is very easy to select an entire image in Photoshop. Just open the image file of your choice, and choose Select -> All from the menu bar, or press the Ctrl + A keys (keyboard shortcut). When you perform one of these actions, you will see an animated dashed border around the entire image indicating that it has been selected.

 

 

Selecting an entire image can be useful for applying different effects, such as colour fills, or surrounding the image with a colour stroke (border).

 

Right click inside the image to see a menu of options foe working with your selection.