Karl,
My photo program has a resize selection under the Edit button. If you just wnat to put a picture in a post I think they are about 4K limit.Pixels, Jamo's thingies can be reduced several ways but I normally take a BMP picture, change it to JPG which reduces the size a huge amount and then use the resizing tool to put it on a post if that is where I want it. Remember that 4K isn't a very large amount of pixels and if the picture is spread out or enlarged it will be fuzzy and grainy. I can't get one out of my gallery using Jammo's method either but I think I missed one of the brackets. Hope this will help along whith what Jamo has already told you.
Ron