Determine Theme's image size requirement

What do you mean by “image size requirement”?

When preparing images in photoshop for proportion and crop to use with a specific theme. I understand that WP will automatically generate multiple sizes and that they can be regenerated when switching themes. I want to know optimum size to begin with. Make sense?

WordPress will not generate multiple sizes for image used in themes. Only for content images uploaded via WordPress.

Ok, thanks.

An example of what I am looking for is found in WP theme twentyeleven, where under: Appearance: Header: it specifies that the header image should be 1000 x 288 pixels.

Many themes do not have this spelled out and I’m trying to figure out how to determine what size image should be. Especially difficult in responsive themes because you can’t pull the image out to the desktop to open in Photoshop to check size. At least I haven’t been able to.

The custom header width & height should be defined in functions.php – either as part of add_theme_support( 'custom-header') or via:

define('HEADER_IMAGE_WIDTH',  xxx );
define('HEADER_IMAGE_HEIGHT', yyy );