Save the files as .jpg extension or .gif extension and open them with your browser to test the file compatibility. Macintosh users will have to use extensions just as their Windows colleagues do. The HTML standard requires extensions on all files expected to be served to a browser. Resizing the Image Resizing is an image editing tool which allows a 6x4 inch photo to fit into a 3x2 inch web space. Resizing uses mathmatical corrections to preserve as much of the image data as it can.
Browsers automatically scale images if the HTML instructions call for that.
You can do better than a browser using image editing software to avoid having pictures resized by someone else's browser. Using Unsharp Mask and Sharpen Edge Unsharp mask works to correct defects created when an image is resized smaller by more than a few percent. Unsharp mask attempts to restore color and contrast distinctions. To use Unsharp Mask correctly will take some experimentation. Sharpen Edge is a complimentary filter for Unsharp Mask.