How would I go about linking to an image on another site without uploading the actual file to my site ? I need to link to some images that are located in a photo hosting site .
Well to display in PhotoPost you would need to upload the file in some other page you can link with a simple html img tag however note you must get the original posters/sites permission before you can link any image from another site.
The other way would be the traditional way of downloading that image there from that site and then reuploading it into your photopost using the traditional upload method.