Configure Blue Iris Motion Detection for ALPR
Option 1: Motion Sensor. You can set the minimim object size (# pixels) to reflect a vehicle image in your camera.
Make sure the default option (Highlight: Do not highlight the motion) is selected. This way, Blue Iris will not include a rectangle in the image it sends to Plate Recognizer.
Option 3: Zones. You can create and edit zones. Just click and drag to set areas of the image.
For more advanced motion sensor options that you may want to try out, refer to the Blue Iris PDF Support Doc. You can view the Support Docs by selecting Help within the Blue Iris application. From there, navigate to Cameras > The Motion Sensor section.