title: Creating django ImageField that is derived from another ImageField in django Models
body: <p>I am creating a django Project where I had Stored a Picture(Image) in database using ImageField as...</p>
  
  <pre><code>original_pic = models.ImageField()
  </code></pre>
  
  <p>Also, I want to Store an Image which will Contain the Same Picture(Image)
  as <code>original_pic</code> with Watermark in another ImageField as..</p>
  
  <pre><code>watermark_pic = models.ImageField(default=watermarkImage())
  </code></pre>
  
  <p>In short, I just want to Apply Algorithm on <code>original_pic</code> and save the result in <code>watermark_pic</code> using django models </p>
  
  <p>Algorithm(Logic) for Applying Watermark to image is as follows...</p>
  
  <pre><code>def watermarkImage(filename, text, color, fontfamily):
      image = Image.open(filename).convert('RGBA')
      imageWatermark = Image.new('RGBA', image.size, (255, 255, 255, 0))
      draw = ImageDraw.Draw(imageWatermark)
      width, height = image.size
      font = ImageFont.truetype(fontfamily, int(height / 20))
      textWidth, textHeight = draw.textsize(text, font)
      x = width / 5
      y = height / 6
      draw.text((x, y), text, color, font)
      return Image.alpha_composite(image, imageWatermark)
  </code></pre>
  
  <p>Note: I know the Algorithm for Applying watermark on Image.</p>