You can visually resize elements such as images, plug‑ins, Shockwave or Flash files, applets, and ActiveX controls in Dreamweaver.
Visually resizing an image helps you see how the image affects the layout at different dimensions but it does not scale the image file to the proportions that you specify. If you visually resize an image in Dreamweaver without using an image-editing application (such as Fireworks) to scale the image file to the desired size, the user’s browser scales the image when the page is loaded. This might cause a delay in page download time and the improper display of the image in the user’s browser. To reduce download time and to ensure that all instances of an image appear at the same size, use an image-editing application to scale images.
When you resize an image in Dreamweaver, you can resample it to accommodate its new dimensions. Resampling adds or subtracts pixels from a resized JPEG and GIF image files to match the appearance of the original image as closely as possible. Resampling an image reduces its file size and improves download performance.