1. A surrounding environment recognition device, comprising: an image acquisition unit that obtains a photographic image from a camera for capturing, via a camera lens, an image of a surrounding environment around a mobile object; an image recognition unit that recognizes an object image of an object present in the surrounding environment based upon the photographic image obtained by the image acquisition unit; an accumulation detection unit that detects accumulation settled on the camera lens based upon the photographic image obtained by the image acquisition unit; a suspension decision-making unit that makes a decision, based upon detection results provided by the accumulation detection unit, whether or not to suspend operation of the image recognition unit; a tracking unit that detects a characteristic quantity in a tracking target image from a specific area in an image captured by the image acquisition unit for a reference frame, determines through calculation an estimated area where the characteristic quantity should be detected in an image captured by the image acquisition unit for a later frame relative to the reference frame and makes a decision as to whether or not the characteristic quantity for the tracking target image is also present in the estimated area; and a resumption decision-making unit that makes a decision, based upon at least decision-making results provided by the tracking unit and indicating whether or not the characteristic quantity for the tracking target image is present, as to whether or not to resume the operation of the image recognition unit currently in a suspended state.