To post from your computer: If your pictures are too large, you have to reduce the size in a photo editing program. There is a pretty good Freeware program that I use, which you can download at www.irfanview.com
(I should get paid for all the advertising I do for them! ).
Open your picture using Irfanview, then go into the Image pulldown menu. Select "Resize/Resample" and in the first set of boxes on the left side of the window, make the largest side of your picture 400 pixels. Generally, as long as the picture is less than 400x400 pixels, you should be fine to post here.
To add the pic to your post (you can only attach one pic per post using this method), just below the Options section in your posting window is Attach File: Click the Browse button and open your picture as you would in any other program.
If you post from your computer and you Preview your picture, you will have to repeat the Browse process. I know that at one point we were having problems with seeing the pic in the Preview, so you may just have to take a leap of faith and just Submit Reply with the picture attached.