title: how to write exif tags with Python in a self generated image
body: <p>I have generated an image with pillow and now I want to add metadata to the image.
  In my image it didn't have a data structure yet, I suppose I have to create one first but how do I do that?</p>
  <p>Reading or changing tags from existing images with exif data structure is very easy with the &quot;exif&quot; tool.</p>
  <p>Every hint is welcome.</p>
  <p>Unfortunately, I am somewhat at a loss and have not yet found any useful information on the Internet.</p>