by ResNet when the region is slightly shrunk. Recall that strict shrink FRIs are the equivalent case of minimal images in humans. Thus, these results demonstrate the existence of many minimal images analogs in DNNs.

Note that smaller FRIs (lower $P$) are much more frequent than larger ones, as observed across the different network architectures and types of FRIs. This trend is expected: one-pixel shifts and two-pixel shrinks are proportionally larger changes for smaller regions, and larger regions generally allow for more high-level features to be included.

We verified that FRIs are not an artifact of the algorithm that resizes the region to the size required by the DNN ($224\times 224$ pixels for VGG-16). We took regions of side length 224 and removed any resizing before input, and we observed that this procedure produces the same results we reported.

Besides the qualitative examples in Figure \[fig:HumanMinImgExample\] and Figure \[fig:DNNMinImgExample\], we display a more varied set of qualitative examples in Figure \[fig:scale\_examples\_supp\]. We observe that FRIs are usually located within object boundaries but can also be found in the background. This is because DNNs are able to recognize regions that only contain background [@zhu2016object], as they have been shown to exploit 