The Beta 1 version of WordPress 3.4 was just released, and one of the new items included is the Flexible Custom Header Sizes feature within WordPress themes. This new feature allows WordPress 3.4 users to easily upload header images. With prior versions of WordPress, themes required header images to be uploaded at a specific width and height. The Flexible Custom Header Sizes feature allows WordPress 3.4 themes to dynamically resize header images to best match with the size of the header.
In prior versions of WordPress, if you didn’t upload a header image with the exact dimensions required (or similarly proportioned), WordPress would require that you crop the image to meet the required proportions (screenshot to the left). With WordPress 3.4, cropping malformed header images is no longer required. Instead, WordPress will stretch the image until it meets your template’s width. Most often than not, wide images work very well when this is done, but tall images do not scale well.
|A header image too tall||A header image too wide|