It took a while to test the gallery extensions that are available to Joomla and that generate thumbnails automatically with shadow and border effects. The free version of the Simple Image Gallery is an excellent extension. The quality of thumbnails is high and a gallery is easily inserted in an article with tags. Below is a demo of the plugin with different file sizes (some pictures may be bigger than your screen when you click on the thumbnail).

 

 

Please note that thumbnails are generated only of jpg files - the gallery does not generate thumbnails from png files and jpg files with spaces in the title also will not work. For example, picture 1.jpg will not work but picture_1.jpg will generate a thumbnail!!

 

Another component is the Phocagallery component (available in the JED) which is particularly useful for larger photo repositories.