HI Cheryl,
How do you want to display the image in the Map Viewer? Do you want to show the image in a pop up or would you like it to be located on the map?
Generally in order to see an image, it will need to be uploaded in order to get a URL. You can do this by uploading the image to any webserver that provides a URL that can be accessed by ArcGIS Online. Additionally, you can add images to specific features from your feature service through attachments and configure the pop ups to display the images.
Here is some documentation regarding methods to add images to pop ups: Configure pop-ups—ArcGIS Online Help | ArcGIS
Cheers,
Kelly
