Requirements

• pip install pillow beautifulsoup4

Summary

This plug-in:

• Adds a style="width: ???px; height: auto;" attribute to any <img> tags in the content, by checking the dimensions of the image file and adding the appropriate style="width: ???px; height: auto;" to the <img> tag.
• Also finds any div class="figures" tags in the content, that contain images and adds the same style to them too.
• If RESPONSIVE_IMAGES setting is true, it adds style="width: ???px; max-width: 100%; height: auto;" instead.
• Corrects Alt text: If an img alt attribute equals the image filename, it sets it to ""

Assuming that the image is 250px wide, it turns this:

<div class="figure">
  <img alt="/static/images/image.jpg" src="/static/images/image.jpg" />
  <p class="caption">
    This is the caption of the figure.
  </p>
  <div class="legend">
    Lorem ipsum dolor sit amet, consectetur adipisicing elit, sed do eiusmod          tempor incididunt ut labore et dolore magna aliqua.
  </div>
</div>

into this:

<div class="figure" style="width: 250px; height: auto;">
  <img style="width: 250px; height: auto;" alt="" src="/static/images/image.jpg" />
  <p class="caption">
    This is the caption of the figure.
  </p>
  <div class="legend">
    Lorem ipsum dolor sit amet, consectetur adipisicing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua.
  </div>
</div>

or this, if RESPONSIVE_IMAGES = True:

<div class="figure" style="width: 250px; max-width: 100%; height: auto;">
  <img style="width: 250px; max-width: 100%; height: auto;" alt="" src="/static/images/image.jpg" />
  <p class="caption">
    This is the caption of the figure.
  </p>
  <div class="legend">
    Lorem ipsum dolor sit amet, consectetur adipisicing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua.
  </div>
</div>