This image lacks the attributes necessary for tracking

I am trying to create a scene inside the Reality Composer to track images.

So I added a cube, an image, and I see this error message

This image lacks the attributes necessary for tracking.

I have tried with different images, same message.

After reading the extensive documentation Apple wrote about the theme (zero lines), I ask you guys what what kind of attributes should the be present on tracking image...

Tips for a successful Image Recognition

You're right, there's no official documentation on that topic. But you can get to the bottom of the truth experimentally. A reference picture you've imported for image tracking has repetitive pattern. If you change it for a proper image you'll never receive such a message again.

Here are some tips for correct reference image attributes:

• Well-discernible pattern
• No repetitive pattern (like yours, or stripes, or polka dots)
• High-contrast edges of silhouettes on a picture
• High-contrast colours (RGB image mustn't be a solid grey if you convert it into B-&-W)
• Moderate size (ideally 480 x 480 pix)
• No white-sheet-image or gradient-only-image
• RGB linear color space
• 72 pixels per inch
• No high compression for JPG
• No alpha channel