Real comparisons of algorithms do not operate on a single image, but large suites of images, where the results are computed as averages. Changing the dataset by

Real comparisons of algorithms do not operate on a single image, but large suites of images, where the results are computed as averages. Changing the dataset by removing one image is unlikely to be a "very real loss." Alternatives exist, and AFAIK Lena is just used as a "canonical" example to use as a nice picture (like the Zachary Karate Club network).