GIF Requirements in Tumblr
Tumblr has specific rules for how you can post photos and animated GIF files on your blog, related to the size and dimensions of your image. When using a GIF image, the most important thing to remember is the file size -- it's unlikely that your animated GIF will exceed the dimension rules while falling under the size requirements.
The maximum size for animated GIF files is 512KB. Anything larger will lose its animation and only display the first frame of the GIF. Upload larger non-animated GIF files. The maximum file size for non-animated photos is 10MB. When uploading multiple photos to a post, the file size limits apply to each image, not the sum of all images.
Any photo larger than 500 pixels across and 700 pixels long are resized down to fit those parameters; if enabled in your blog's settings, Tumblr will share a link to the higher resolution photo. Animated GIF files cannot exceed 500 pixels wide, otherwise they will lose their animation when posted.
Tips for Lowering GIF Size
If you're creating a GIF and having trouble reducing the file size, try reducing the dimensions of the file to lower the size. Cutting back on the number of frames in the image will also lower the size, though it may cause your animation to be less smooth. Reducing the color palette -- from the maximum 256 colors -- will also help create a smaller file, though it will also reduce image quality.
Share GIF images in one of three ways. Sharing a GIF in the body of a post from an external source, using the photo button on the rich-text toolbar, circumvents Tumblr's photo rules, but it's only available on certain posts and does not display the image automatically on the dashboard. Upload photos into the body of text posts by clicking the "Upload Photo" button in the upper right corner above the text box. Images can also be uploaded via photo posts, which can include up to 10 images.