We are comparing the features of two images of the same person using two different cameras, and would like to determine the level of similarity between the two images. We have already used the Bland-Altman plot, which confirms that the two are not dissimilar. Linear-regression shows that there is a close relationship. However, we are not sure if this translates to 'being similar'. 

Tests such as Anova is not appropriate as there are large inter-subject variability. 

What would be a suitable method to test if the features of the images from the two cameras are similar? 

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