There is no other way to upload a photo to a post on Whatbird directly from your computer. You can use the Whatbird Gallery, but it is similar to using a site like Flickr in that you have to get the URL and paste it into your post. I don't know how much photo storage space the Whatbird Gallery allows, but I haven't run out yet. Just remember that there is no option to delete a photo in the Whatbird Gallery, you can only replace it with another photo. Because of this I recommend using a photo sharing site or something like Google Photos instead.