Unsupervised Anomaly Detection in Images
There seems to be a clear line between samples with anomalies and those without. Label them and run a classifier? e.g SVM. One shouldn't use more complex models than needed.

Also, be a bit careful with trying to detect all kind of anomalies. It's not always realistic and might lead you away from more straightforward, and perhaps better solutions.

You could also try something as simple as a histogram from one part of the image. Looks like it should be able to find the anomalies.