Visualizer fails with a PolicyError

[lukehsiao]

Describe the bug
This is a known bug caused by a recent change to ImageMagick and can be resolved by editing the policy file.

To Reproduce
In the tutorials, it will fail on this display call:

from fonduer.utils.visualizer import Visualizer
from hardware_utils import entity_to_candidates
vis = Visualizer(pdf_path)

# Get a list of candidates that match the FN[10] entity
fp_cands = entity_to_candidates(FP[10], test_cands[0])
# Display a candidate
vis.display_candidates([fp_cands[0]])

Error Logs/Screenshots
The user will see an error like:

PolicyError: not authorized `data/pdf/bc546-d.pdf' @ error/constitute.c/ReadImage/412
If applicable, add error logs or screenshots to help explain your problem.

When the Fonduer visualizer tries to display the PDF.

Additional context
The bug tracker for the issue on launchpad can be found here:

https://bugs.launchpad.net/ubuntu/+source/imagemagick/+bug/1796563

the change was introduced as a more secure default in the underlying package.

Work-around
A workaround for now is to simply change the policy in /etc/ImageMagick-6/policy.xml for PDFs to read.

<policy domain="coder" rights="read" pattern="PDF" />

[HiromuHota]

I also noticed this issue. The workaround that I took for Docker is to remove the file.
https://github.com/HazyResearch/fonduer-tutorials/blob/v0.6.2/Dockerfile#L14