Which AR asset is right for my barebones needs?

Hey! There are a number of AR libraries, toolkits and assets available but they all provide way more functionality than I need.

I need to create my own images/symbols/markers and have a function that triggers when the images appear in front of the camera.

I don't need an overlay. In fact I don't even want to show what the camera sees.

Multiple images/markers/symbols being detected at once is not quite necessary but would open up a lot of possibilities.

Is there anything this barebones? Which toolkit implements these basic simple things the easiest way?