Images are a critical ingredient to great looking websites. A typical site will incorporate numerous images in a wide range of sizes and formats. Each image file format (such as JPG, PNG and GIF) has it's own virtues and capabilities. For example GIF files can contain animations.
Today we have access to an assortment of professional-grade image manipulation products and tools, both free and commercial. At the very least your chosen image tool software should be able to crop, scale, rotate, resize and adjust the colour balance of an image. And be able to save it in a variety of image formats.
Applying advanced techniques such as colour fades and tints, rounded edges and shadows, blurs and soften effects, masks and layers, will add a touch of class and individuality to your page banners and inline images.
The ever popular Adobe Photoshop product range has many fans. Fans who have generated a wealth of web-located tutorials, in both written and video formats.
Photoshop isn't free, but there are many open source alternatives, including the immensely powerful GIMP editing tool. Version 2.8 sports a more intuitive single-window interface. It can be downloaded from the GimpShop website, where you can also see how it in action via these tutorial videos).