This seems like it must be a permissions issue on my machine. After a systems update on Windows 10, when I run:

import matplotlib.pyplot as plt
#make figure
plt.plot([1,2,3,4])
plt.ylabel('some numbers')

#save
plt.savefig("./figs/my_plot.jpg")

It will create the figure the first time the code is run. If I make a change to the code (e.g. change label) and then re-run, the plot shown in a Jupyter Notebook is updated, but the file saved on my machine is not! This is a new issues as of today, after a systems update was pushed out, so this seems like a likely culprit. Any insight for me to fix this issue, besides creating a new file name every time a change is made?

TLDR: The photos WERE being overwritten, but the date was kept the same as the original file, due to a quirk of windows when a folder has lots of photos.

Jon's answer from 10/2/2015 did the trick for me. https://superuser.com/questions/147525/what-is-the-date-column-in-windows-7-explorer-it-matches-no-date-column-from/335901#335901

Basically windows detects lots of pictures in a folder and "optimizes" said folder for pictures. This means the column displayed is Date rather than Date Modified as it would be for a folder "optimized" for documents. Date takes the earlier of Date Created and Date Modified. As Date Created doesn't change when matplotlib .savefig overwrites a file the Date column never changes.

To resolve this issue I customized the folder for documents. To do this select the folder and open the properties window. Navigate to the customize tab then select documents under "optimize this folder for."