An imaging system may include an image sensor and a transparent protective layer formed within the field-of-view of the image sensor. The imaging system may include a light source that emits light in a predetermined pattern. The imaging system may include circuitry that may detect a reflected version of the predetermined pattern of light in image data captured by image sensor. In response, the imaging system may determine an obstruction is present within the field-of-view of the image sensor. The obstruction may be located on the transparent protective layer and may be within 10 centimeters of the image sensor. The light source and image sensor may be located in the interior of a vehicle and oriented to face the exterior of the vehicle. The imaging system may use the image data captured by the image sensor to perform vehicle assist functions for the vehicle.