The image data for a picture is specified with the <a:blip> element within the <pic:blipFill> element (BLIP = binary large image or picture). Note the namespace used is xmlns:a="http://schemas.openxmlformats.org/drawingml/2006/main". The image data can be stored locally within the same file, or linked to a location outside of the file. The state of compression for the data is also specified. All of this information is contained within the attributes for <a:blip>.
Specifies the compression state with which the picture is stored. Possible values are:
Specifies a relationship in the .rels part for the part that references the picture. For example, the sample above has r:embed="rId4". That relationship is shown here:
And the image file within the package is shown below:
Specifies a relationship in the .rels part for the part that references the picture. It is used to specify an image that does not reside within the package.