raise ValueError('Image with id {} already added.'.format(image_id)) in Tensorflow object detection api

In the ssd_mobilenet_coco_v1.config file, num_examples was 8000. In my case, test dataset only has 121 samples. I forgot to update that and got new kind of error that I couldn't find on the Internet. As it is a silly mistake, so I think a very few people did that. this answer might help someone who will do this kind of mistake. I changed the following in the config file and the error is resolved:

eval_config: {
        #num of test images. In my case 121. Previously It was 8000
        num_examples: 121
        # Note: The below line limits the evaluation process to 10 evaluations.
        # Remove the below line to evaluate indefinitely.
        max_evals: 10
      }