To upload a photo blog post on Tumblr, first navigate to Tumblr.com in your web browser and either create an account or log in. From your dashboard, click the "upload a photo" button and select a photo from your files or take a new photo with your camera. You can add a caption to your photo and tags to help others find your post more easily. Finally, click "Create post" to upload the photo blog to your Tumblr account.