Most digital cameras these days produce very large images; a 12MP camera for example will generate images that are 4000 x 3000 pixels in size. This is great if you want to produce high quality prints, but for other applications these huge images are simply too big. One common example is publishing images on websites. Most web images are no bigger than 600 or 800 pixels wide, so in order to prepare a digital photo for display on a website you will need to resize it, and you may also need to produce thumbnail-sized versions of the same pictures. This isn't a problem if you're talking about one or two pictures, but if you want to add an entire album of photos it would be very tedious and time-consuming to resize each on individually.
Fortunately Adobe Photoshop has a feature called Batch Processing, in which an action or series of actions can be recorded as a process, and then automatically repeated for a large number of images. This is immensely useful and not too difficult to accomplish.
The first step is to activate the Actions palette. In the Window menu, click on the Actions item, or use the default keyboard shortcut Alt+F9. A new palette should appear in the palette area on the right of your screen, with a tab labelled Actions.
This is the means by which you can record and edit a series of actions such as image resizing, exposure adjustments, changes to colour space or any other image processing function from Photoshop's menus.
To start recording your process, click on the small menu icon in the upper right corner of the Actions palette. On the drop-down menu that appears, select New Action.
A dialogue box will appear inviting you to name the new action. It's a good idea to name it something descriptive and easy to remember, because it will appear in a list alongside a number of default batch processing operations, so just calling it "Action1" isn't going to be much help. You can also assign the new process to a function key, which could be useful if it is a complex process that you often carry out.