Usually, many of the ready-to-use image sliders (check the best ones in the galleries category) require a specific width-height for a good looking output.

If your images don't have a standard size, jQuery Image Scale Carousel can be for you.

jQuery Image Scale Carousel

It is a jQuery plugin which auto-scales the images into appropriate height and width keeping their aspect ratio.

The plugin simply converts an array of images to a slider and supports manual browsing with previous-next controls and auto-play.

The download package also includes a PHP-based example which creates the "images array" itself by scanning a given directory.

WebResourcesDepot Feed