What images are allowed:

• png
• jpg
• jpeg

Maximum Size: smaller than 1 MB!
If your image is bigger than 1 MB, them you can use this online tool to reduce the size:
https://tinypng.com/

NOTE1:
Upload the images via /administrator.
Go to Media and upload the images to the correct folder:

NOTE2:
Each category has subcategories (like the city name) and all these city names have one or more subcategories that you can identify as an address.

How to go there:
Open the administrator page:
/administrator/
login with you username and Password
Then open the Media folder <images/project-references>