Many suppliers send their images out in all shapes and sizes. These can be hard to work with sometimes as websites and quote software can sometimes do strange things with long and wide images.
They are also all various file sizes and resolutions and generally have little consistency
Generally a website promotional product image will not need to be more than 500×500 pixels at a resolution of 72dpi.
There are various pieces of software that can resize your images on mass. None work with quite the same finesse as photoshop though.