The technology relates to detecting possible imaging sensor occlusion. In one example, a system including an imaging sensor and one or more processors may be configured to capture first image data using the imaging sensor. The one or more processors may encode the first image data into an uncompressed image file and generate a compressed image file based on the uncompressed image file. The file size of the compressed image file may be determined and based on the file size of the compressed image file, the system may determine that the imaging sensor is possibly occluded.