I am sorry it took me so long to reply. I have really been in a lot of directions these days.
When you open a picture on your computer, it usually opens in a program where you can do changes to the picture such as crop or color correct or size. Every program is a little different and has different ways to adjust.
The limitations here on the site are 128kb That means you need to have the file size smaller than that or they will not upload. Otherwise you could just put a link to a photo in your Picasa album so people here can go to the picture. This will only show up as a link in your post.
You really need to look into the program on your computer and figure out how to size the pictures down. Perhaps if you mention the program here, someone else with the same one will be able to help guide you through the steps. I use Adobe Photoshop and if you have that one, I will help you out too.
Let us know how you do please. I know this isn't much of a help, but it will get you on the right track.
Sheila