Postwaves is not a content host, thus you need to host the content outside of Postwaves, and then submit a link to that content (.jpg or .png).

 

If the image is already hosted on the web:

Right click the image, select "Copy Image Location" [PC] or “Copy Image Address” [Mac] and paste the URL into Postwaves’ “Add Post” “Image” field.

 

If you would like to upload your own image, please follow the instructions below:

Go to http://imgur.com (no need to create an account)
Click on
Drag or select Image from your computer
Click “Copy” to copy image URL
Paste URL into Postwaves’ “Add Post” form