from pptx import Presentation

prs = Presentation('template.pptx')

slide4 = prs.slides[3]

for shape in slide4.placeholders:
    print('%d %s' % (shape.placeholder_format.idx, shape.name))

>>>
0 Title 3
10 Picture Placeholder 7

placeholder = slide4.placeholders[10] # idx key, not position
picture = placeholder.insert_picture('test.jpg')

File "C:Python273libsite-packagespptxshapesplaceholder.py", line 323, in insert_picture
pic = self._new_placeholder_pic(image_file)
 File "C:Python273libsite-packagespptxshapesplaceholder.py", line 334, in _new_placeholder_pic
rId, desc, image_size = self._get_or_add_image(image_file)
 File "C:Python273libsite-packagespptxshapesplaceholder.py", line 345, in _get_or_add_image
image_part, rId = self.part.get_or_add_image_part(image_file)
 File "C:Python273libsite-packagespptxpartsslide.py", line 42, in get_or_add_image_part
image_part = self._package.get_or_add_image_part(image_file)
 File "C:Python273libsite-packagespptxpackage.py", line 50, in get_or_add_image_part
return self._image_parts.get_or_add_image_part(image_file)
 File "C:Python273libsite-packagespptxpackage.py", line 159, in get_or_add_image_part
image_part = self._find_by_sha1(image.sha1)
 File "C:Python273libsite-packagespptxpackage.py", line 171, in _find_by_sha1
if image_part.sha1 == sha1:
AttributeError: 'Part' object has no attribute 'sha1'

prs = Presentation()
slide = prs.slides.add_slide(prs.slide_layouts[8])
placeholder = slide.placeholders[1]  # idx key, not position
picture = placeholder.insert_picture('test.jpg')
prs.save('new.pptx')