I apologize to Mac users because this focuses on Windows PC options.
I don't own a Mac. If anybody out there wants to buy me a new one, I will be happy to throw together some suggestions for that platform, too.
It's fairly easy to resize (and compress) a photo using MS Windows Paint. Also, it's built into Windows so doesn't cost anything to use (except your time, of course.)
1. Open Paint and then open your photo file
2. Use the Resize Tool
If you have Microsoft Office installed, you most likely have The MS Office Picture Manager (MSO PM) tool available, too.
1. Right-click on the file and select "Open With" | MS Office
2. From the menu, select "Edit Pictures"
3. Use either the "Resize" or "Compress" tools to the right
4. I have found it best to use the "Resize"
5. Select one of the Predefined Width x Height options (best for this board is "Web - Large 640 x 480")
Save your photo (or use the "Save as...[different file name]" so you can save the smaller version as a copy and keep the original file intact.)
As it downloaded from my camera, the photo below is gihumongous. It's too big to upload here. If it did upload, it would take a very, very long time to upload and it would eat your monitor.
The version below was resized to Web - Large using MSO PM
the whole process takes only a few minutes. with practice, you can resize several pictures, one after the other, in just a few seconds each.
To see examples of other versions of this picture, please check out this page:
Trust me when I tell you that mastering this important skill is much easier than trying to achieve a stinkin' scant quarter-inch seam.