Are both of these HTML attributes needed for image or, if i just put in the height attribute is that going to cause issues for some surfers?

The reason im asking is that i have a whole heap of images that have a height of 1024 but the widths all vary greatly, if i cant have a set height and width, is simply adding the height actually going to do anything or should i leave that out in addition to the width?

Im guessing its not really going to make much of a difference but i could be wrong so was hoping some of you folks could offer some advice, is something better than nothing when it comes to image dimensions in HTML code?

Regards,

Lee