I realized that PowerPoint is removing all image metadata (PNG). In my case the metadata contains the data from which the image was generated. (chemical structure). The idea would be to put these images into presentation but still be able to later extract the information. However this fails because PowerPoint removes it.
Is there a setting to make power point conserve custom metadata?
EDIT 9th November:
I've learned that when looking at the content of the pptx file (unzip) the original image with all metadata is present. However once you export or copy it from within the presentation, it's "converted" loosing said metadata.