Xcode 8 will automatically recognize any images you’ve got in an Asset Catalog and offer them up as a suggestion inside of a UIImage initializer.
So basically what you need to do is just the following (as you have done in your question, but there must be something else that´s disturbing it):
let i = voiture // image name
And then just use
i when you want to set an image.
Under the hood it’s creating code that looks like this:
#imageLiteral(resourceName: "voiture.png"). But inline in the source editor, you’ll just see the file name of the image.
Note that you need to click on the instellisense suggestion so that you see a thumbnail of the image in the code and then the image name.