Support for .MPO images

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Currently, .MPO images are not supported.

I took a photo with an iPhone in portrait mode, which encodes images in .MPO format: https://fileinfo.com/extension/mpo

Although the picture was saved in .jpeg extension, it is .MPO encoded and cannot be parsed by pptx. As this is a pretty popular technology in smartphones, probably it makes sense to support this.

Here is the error I got: (ValueError("unsupported image format, expected one of: dict_keys(['BMP', 'GIF', 'JPEG', 'PNG', 'TIFF', 'WMF']), got 'MPO'"), False)