How to Maximize a Picture in a Photoset in Tumblrby Andrea Ruiz
Tumblr's photoset feature enables you to embed clickable thumbnail galleries of up to 10 images from your hard drive into your blog posts. By dragging and dropping the thumbnails while creating your photoset, you can resize the image thumbnails to display within the dimensions of a Tumblr dahsboard. However, if you'd like to feature an image in a photoset in the largest possible thumbnail size, you must ensure that it appears in its own row.
Select the blog to which you want to post your photoset from the drop-down menu on your dashboard, if your Tumblr account manages more than one blog. If you have only one blog, your Tumblr account publishes all of your posts to it by default.
Click the "Photo" icon to create a new photoset post.
Click the camera silhouette icon in the post pop-up form, and then browse your hard drive for your first photo. Double-click the image file to automatically upload it to your Tumblr.
Click "Upload Another Photo" to browse your hard drive for the second image. Double-click the image to upload to your photoset, and then repeat the process for any additional images.
Click and drag with your cursor any photos you want to minimize next to the other images you want to minimize, until a blue line appears next to the second image. Release the cursor to drop the first image next to the second image. Tumblr automatically generates a row of thumbnails for your photoset gallery, with up to three images per row.
Click and drag with your cursor any images you want to stand alone at the maximum size possible in the photoset, so that the image occupies its own row. To remove any image from row of thumbnails and maximize its size in the photoset, click and drag it to its own row.
Add any text description, formatting and tags to the post, then click the "Post" button to publish your photoset to your blog.
Tumblr allows you to upload photos in only JPG/JPEG, GIF, BMP or PNG format, no larger than 10MB in file size per photo. Animated GIFs may be up to 1MB in file size and no larger than 500 pixels wide.