PowerPoint is slowly adding features that have been standard in Photoshop for years. One useful one is the image blur filter to increase depth of field of your photos ( earlier post). It adds some extra realism to this composite image trick (discussed earlier here and here)

1. Find an image for the foreground and use the PowerPoint format/remove-background function to get rid of the white background
2. Find a background (nice image of Cafe de Flore by DarkB4Dwan)
3. Combine the 2 images
4. Blur the background with (click the image, format, artistic effects, the right one in the 2nd row)