How Do I Classify Dirty/Dusty Camera Images? I would like to test (predict) whether camera images are dusty/dirty or not.; a classification task indeed.

The question is about finding the most appropriate Machine Learning approach, perhaps any suggestions for possible Deep Learning methods specifically tailored for this particular problem?
What kind of distortion does dirt/dust produce? If it is somewhat regular, for example more or less regularly sized speckles (greyish circles) it might be worthwhile to try to classify the logarithm of the real part of the fourier transform of the picture, instead of the original picture.

Also, knowing the physical properties of the distortion might guide you towards devising simple heuristics (for example based on some frequencies in the fuorier spectrum) that are as good as a ml-based approach.