Uploading large image on Article content type results in 500 server error

Steps to reproduce:

a) Install Drupal 8.2.x on simplytest.me (we used 8.2.5).
b) Choose the Standard install profile (and we used English language)
c) After installing, click on an Add Content link, and add a new Article.
d) In the Image field, select an image from your computer that is larger than the stated max size of 2MB.
e) Fill in the title, body, etc.
f) Attempt to save the Article.

What I would hope to see is a friendly message saying that my image was too large.

What I see instead is a 500 server error page.

Note: I tried this on my local machine, using 8.2.x (not sure exactly how old but at least the same branch), and when I attempted to put the image into that field (also with a 2MB limit on my machine), I got a message right on the screen saying:

The file could not be saved because it exceeds 2 MB, the maximum allowed size for uploads.
File upload error. Could not move uploaded file.

This did not happen on simplytest.me.