Office has picture adjustment tricks to convert a picture into something gray and transparent.
We found a black & white photo (rights free) online and used the Office Picture Tools | Format | Remove Background to make the surrounding transparent and show through the page background color.
Color to Grayscale
For a color photo, switch it to ‘black and white’ using Picture Tools | Format | Adjust | Color | Color Saturation | 0%
Picture Transparency is a new Office 365 feature that is very useful here. Picture Tools | Format | Adjust | Transparency.
Use it to let some of the page background color show through the image.