I am not fully familiar with the way jpegs compress but it's something like
this;
A completely black image saved as a jpeg will have a very small file size.
An image composed of many colours randomly disorganised in disorganised
patterns will have a very large size when saved as jpeg. This is because
jpeg compression somehow uses a lack of variation between pixels to produce
it's compression. The less variation between pixels the smaller the image
size. For some reason rotating an image 90 degrees and saving it may also
produce a different file size to saving it unrotated.

Pete

"Pete Stockdale" <Pete@pjcactus.freeserve.co.uk> wrote in message
news:bbthd0$1n6$1@news8.svr.pol.co.uk...
> Novice question - answer in simple terms requested...
>
> Just taken some shots of flowers in a greenhouse - with same settings the
> picture file size (jpg) varies between 157 and 218kb - why is that?
> Thanks.
>
>