If your Tumblr blog isn't already showing full-sized images, you can get rid of the thumbnails with just a few tweaks. As long as your photo files are no larger than 10 MB in size and are in JPG, PNG, or BMP format, they can be displayed in full resolution. If you have more than one blog, you will have to check the template HTML code to ensure it works for whichever blog you're using.
Enable High Resolution Photos
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Step 1
Log into your Tumblr account and click the gear-shaped "Settings" button.
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Step 2
Click the "Dashboard" link.
Step 3
Check the "Show Full Size Photos" button in the dashboard options. This option will show full size photos on your dashboard.
Step 4
Click on the name of your blog in the right menu, then click the "Edit Theme" button.
Step 5
Click on the "Edit HTML" button under the template image on the left-hand side of the screen. Locate the tag "{block:Photo}" and add "{block:HighRes} {/block:HighRes}" on the same line. Exit and save your changes in the "Preferences" screen by clicking on the "Save Settings" button on the bottom-left. This change will adapt the template to accept larger, high-resolution images.
Upload an Original-Size Image
Step 1
Click on the "Photo" icon on the top of the main screen to add an image entry.
Step 2
Upload a photo either by finding the photo on your hard drive or typing in the URL where the image is hosted into the same line.
Step 3
Click on the "Create Post" button on the bottom-left. The picture will appear on your blog with its original dimensions.