Many of my client websites require an image gallery to show multiple images sorted by category or album. One of my favorite options is the Joomla Component JoomGallery. It offers a great rotating image module, automatic thumbnail resize and the ability to show the large images in a popup, lightbox or slideshow window. Joom Gallery is currently available for Joomla 2.5 and Joomla 3.4.
The following video tutorial will show you how easy it is to add images to the gallery and have them live on your site in no time.