Tumblr Picture Size in Posts and Linksby Randall Blackburn
You can publish pictures and images in Tumblr photo and text posts. You can also publish links to external images using a Link post type. Tumblr posts support PNG, BMP, JPG and GIF image formats. Most Tumblr themes allocate 500 x 750 for images in posts, so stay within these dimensions to display the original images in your posts. For larger images, your viewer can click on a thumbnail in the post to view the large version displayed in a 1280 x 1920 window. Tumblr imposes a few additional size restrictions for photos displayed in posts.
Tumbr Image Limitations
A photo post can contain up to 10 images, however, the total file size for all images in one post cannot exceed 10MB. Note that limitations apply only to uploaded photos, and not photos you link to with a URL. There are no limitations in size or dimension for linked photos. Tumblr simply displays linked photos in the default Tumblr image viewer, which automatically sizes the image for the post.
Animated GIF Images
Tumblr imposes different limitations for animated GIF images. Animated GIFs are limited to a width of 500 pixels and a file size of 1MB. Though you can upload larger animated GIFs on the platform, the image will display as a static picture, and the animation will not play.