I use Microsoft picture manager and my pictures come out way bigger than I intend, even when reduced to below the size limit listed on our site. I need to do some more research and experimentation in the testing area to figure this out.
On CRG we're limited to a single image file size of 200 Kilobytes (which isn't very large), and a total post image size (for up to 4 images) of 500 Kb. For each of your images, the first thing to do is to 'crop' the image area to the region that is needed to show whatever it is you want/need to show. That will provide a small measure of file size reduction with a corresponding reduction in image area on the screen.
There are two other issues re image size, and you need to be conscious of both of them.
1) How large the image is on your screen is a function of the
image resolution in pixels (horiz, vert) and your screen resolution. Each of us have control of screen resolution on our computers. For the image resolution, approx 800 h and 600 v is a good choice for most of us; it will be large enough for viewers, but shouldn't be larger than our entire screen (unless your screen resolution is set for something old like VGA 640x480 format)..
2) Second is
File Size which you can check via 'file properties' on your computer. This must be smaller than 200 Kb to post to CRG. File size is related to the image size (h, v), but is not a fixed relationship due to jpg compression). Image compression by techniques such as JPG greatly reduce your file size while maintaining your original image resolution in pixels (at a slight cost in image quality); if done correctly you probably won't be able to see any loss.
Additionally, using file/image size reduction software such as '
Light Image Resizer', you can maintain a good screen based image resolution, AND reduce the file size even smaller than what your original jpg file was, in only a jiffy...
You can download a 'free personal use copy' of Light Image Resizer here.
http://www.obviousidea.com/windows-software/light-image-resizer/