I by accident photographed with a digital camera a single grey saucer like object with ridges and an oblong portal

The night of the sighting the weather was a low cloud cover and medium to high wind.  There was a moon but it was not visible that night and was far to the east at that time.  I am a public works Inspector and was documenting work a contractor was performing on a signal pole.  I was looking up at the work on the pole and the sky beyond the pole was dark and no image in the sky could be seen with my normal vision.  After taking a digital picture of the pole it was immediately noticed that an image appeared in the background.  The digital camera caught a single grey saucer like figure.  I continued my normal schedule of work for the night and later went back to my office to download the photos.  On my computer screen it was clear that the object had form, shape, distinctive ridges on the outside and an oblong portal.  This photo was taken completely by chance whereas myself and eight others working that night were not aware it was there.