I need to achieve that 20 images are at the same level in PowerPoint without adjusting each of them. How do I do this?
As discussed in the comments above the option you are looking for is called "Align left" / "Align Top". In PowerPoint 2010, you need to select all images and then go to
In PowerPoint 2003 it can be found on the "Drawing" Toolbar under "Draw/Align or Distribute". If you knew where to find it in 2003, to find out where it went in PP2010 have a look at the page
The Excel2010 spreadsheet linked there contains the answer: