Switch off picture compression - PPT 2013

If you want to change the default picture compression for the current presentation, click File -  Options - Advanced - under image size and quality, check the option Do not compress images in file. 

If you want all files to not compress you will have to edit the registry.
Press the Windows key on your keyboard in combination with the letter R. In the dialog, type regedit en click OK.

Navigate to the key
HKEY_CURRENT_USER\Software\Microsoft\Office\15.0\PowerPoint\Options.
Right click and choose New, add a new DWORD value. Give it the name AutomaticPicturesCompressionDefault. Check it, it has the value of 0 to disable the automatic compression, or 1 to enable compression. Finally close the registry editor.