Adding picture in content placeholder python

Question

I would like to add a picture into a content placeholder in pptx using python. I'm forced using the company template, which uses the content placeholders for some pictures. How do I add a figure into a content placeholder?

Is there an attribute in the content placeholder object, to insert a picture? I have 'guessed' one, which does not give an error but also does not import a figure (see below).

As a workaround, is there a simple way to replace the content placeholder with a picture placeholder, keeping all dimensions and positioning the same?

from pptx import Presentation

prs = Presentation('blank_template.pptx')

################
# Currently only possible to append, not insert halfway the presentation for instance. Thus removal of slides is necessary. 
#####
# Layout numbers:
#
# 0 Title slide
# 1 Title and content
# 9 Section header
# 16 Comparison
# 19 Title and 4 pictures
# 
########################
#
# Placeholders
# 
# layout 1
#   0 Title 1
#   1 Content Placeholder 2
# 
# layout 9
#   0 Title 1
#   1 Text Placeholder 2
# 
# layout 16
#   0 Title 1
#   1 Text Placeholder 2
#   2 Content Placeholder 3
#   3 Text Placeholder 4
#   4 Content Placeholder 5
#
# layout 19
#   0 Title 1
#   1 Picture Placeholder 2
#   13 Picture Placeholder 3
#   14 Picture Placeholder 4
#   15 Picture Placeholder 5
#   16 Text Placeholder 6
#   17 Text Placeholder 7
#   18 Text Placeholder 8
#   19 Text Placeholder 9
#
##########################

#table of content
Header1='First content'
Header2='Second content'

#Slide 1;
#table of content
slide_layout = prs.slide_layouts[1]
slide = prs.slides.add_slide(slide_layout)
title_placeholder = slide.shapes.title
title_placeholder.text = 'Table of Content'
placeholder = slide.placeholders[1]  # idx key, not position
placeholder.text = Header1

#Slide 2;
#header 1
slide_layout = prs.slide_layouts[9]
slide = prs.slides.add_slide(slide_layout)
title_placeholder = slide.shapes.title
title_placeholder.text = Header1


#Slide 3
#text block
slide_layout = prs.slide_layouts[1]
slide = prs.slides.add_slide(slide_layout)
title_placeholder = slide.shapes.title
title_placeholder.text = Header1+' - text block'

#Slide 4
#comparison figure
slide_layout = prs.slide_layouts[16]
slide = prs.slides.add_slide(slide_layout)
title_placeholder = slide.shapes.title
title_placeholder.text = Header1+' - comparison'
placeholder = slide.placeholders[1]  # idx key, not position
placeholder.text = 'image 1'
placeholder = slide.placeholders[2]  # idx key, not position
image= 'my-image.png'
placeholder.picture= image
placeholder = slide.placeholders[3]  # idx key, not position
placeholder.text = 'image 2'
#placeholder = slide.placeholders[4]  # idx key, not position
#picture = placeholder.insert_picture('my-image.png')

#slide 5
#4 pictures
slide_layout = prs.slide_layouts[19]
slide = prs.slides.add_slide(slide_layout)
title_placeholder = slide.shapes.title
title_placeholder.text = Header1+' - 4 pictures'
placeholder = slide.placeholders[1]  # idx key, not position
picture = placeholder.insert_picture('my-image.png')
placeholder = slide.placeholders[13]  # idx key, not position
picture = placeholder.insert_picture('my-image.png')
placeholder = slide.placeholders[14]  # idx key, not position
picture = placeholder.insert_picture('my-image.png')
placeholder = slide.placeholders[15]  # idx key, not position
picture = placeholder.insert_picture('my-image.png')

prs.save('updated.pptx')