How can you allow a user to select an image to be used as a texture in game?

Is it possible for a user to be able to select an image file from their computer to be used as a texture in game and actually change the material?

I'm fairly new to Unity, but I have a lot of experience in related programs. I'm not sure how to approach this and any help would be appreciated!

 

Sure it's possible. Load the image file with ImageConversion.LoadImage, then just apply it to the material (probably as the mainTexture).