Adding images to your app that are eligible for image tracking is relatively straightforward. The most important part is that you pay close attention to the images you add to your app. It's up to you to make sure that the images you add are high-quality and well-saturated. ARKit will scan for special features in an image to try to match it, so it's important that your image has enough details, contrast, and colors. An image of a smooth gradient might look like a recognizable image to you, but it could be tough for ARKit to detect.

To add images to your project, go to the Assets.xcassets folder, click the + icon in the bottom-left corner, and select New AR Resource Group, as shown in the following screenshot:

After adding a new resource group, you can drag images into the folder that was created. Each resource group will be loaded and monitored by ARKit all at once, so make sure you don't add too many images to a single resource group because that could negatively impact the performance of your app. Apple recommends you add up to about 25 images to a single resource group.

After you add an image to a resource group, Xcode will analyze the images and warn you if it thinks something is wrong with your image. Usually, Xcode will inform you as soon as you add a new image because ARKit requires the physical size of the image you want to detect to be known. So if you're going to detect a specific painting or a page in a magazine, you must add the dimensions for these resources in centimeters as they exist in the real world.

The start project from the code bundle comes with a couple of prepared images that you can explore to see some examples of the kinds of images that you could use in your own apps.

Once you have found and added some excellent content to use in your AR gallery, it's time to build the experience itself.