1. Simple to Magical Works with Office 2010 and above

2. Free image from Office Online

3. Photo of cloudy sky Captured by Dr Nitin. You can use it
Photo of cloudy sky Captured by Dr Nitin. You can use it. No royalties 

4. Magic

5. DO NOT click Wait… Steps
Remove Background from the windows in the photo
Position the photo so that the top left of the left side window aligns with the top left of the slide
Picture Tools – Color – Grayscale
Enlarge the sky and put it behind the photo
The sky should be much larger than the width of the slide
Position it in such a way that the lower part is behind the windows
Put Motion animation from right to left
Remove Smooth Start, Smooth End settings from Animation Effects Options
Increase duration to 30 sec
Change animation to Start with Previous
Change Repeat to Until Next Slide

6. DO NOT click Wait (5 sec) This variation was suggested by my friend and ace photographer, Anindo Ghosh
Steps
Remove Background from the windows in the photo
Position the photo so that the top left of the left side window aligns with the top left of the slide
Enlarge the sky and put it behind the photo
The sky should be much larger than the width of the slide
Position it in such a way that the lower part is behind the windows
Put Motion animation from right to left
Remove Smooth Start, Smooth End settings from Animation Effects Options
Increase duration to 30 sec
Change animation to Start with Previous
Change Repeat to Until Next Slide