Firstly, I would NOT modify any original file, nor would I set my camera to take lower resolution images. Take the best quality picture you can. They can be edited later.

Having said that,

I like to use a tiny program called "Picture Resize". Seems to work on all versions of Windows.

Download it from here:  http://www.rw-designer.com/picture-resize  Click on the link named "PhotoResize400.exe"  right below the heading " How to use it? " .....or.....click here to download directly: http://www.rw-designer.com/NT/6.0/PhotoResize400.exe

Once installed, you will find a new icon on your desktop named: "PhotoResize400.exe"

Right click on this icon and choose "Rename". Rename to "PhotoResize800.exe"  This will resize any picture to a maximum dimension of 800 pixels on the longest side of the image. This is usually sufficient to upload to NAT.

How do I resize my photos?

Very simple. Just click and drag your photo on top of the PhotoResize800.exe icon and let go. Choose RUN, then press ENTER when asked to in the black window. You will now see a resized version of your photo. You can identify the resized image by it's filename. The program will add the numbers 800 to the end of the filename. So a photo named "tractor" will now be "tractor-800". That's it. You can now upload this file to NAT.

BTW: You can also drag and drop a folder of images onto the icon. It will then process and resize all of the images inside of it.

More instructions on the website:  http://www.rw-designer.com/picture-resize 

For advanced users:

There are other variables that can be replaced in the filename to enable different operations.

 

Name codes overview

Resizing method

• PhotoResize400.exe - maximum side 400 pixels.
• PhotoResize_400.exe - minimum side 400 pixels.
• PhotoResizeF400x300.exe - frame size of 400x300 pixels. The resulting image width will be smaller or equal to 400 and its height will be smaller or equal to 300 pixels.
• PhotoResizeW400.exe - width set to 400 pixels. Height automatically computed to keep aspect ratio.
• PhotoResizeH400.exe - height set to 400 pixels. Width automatically computed to keep aspect ratio.
• PhotoResizeP50.exe - resize to 50%.
• PhotoResize400x300.exe - resize to exactly 400x300 pixels. Aspect ratio is not preserved.
• PhotoResizeD100.exe - resize to 100DPI. Physical size stays the same.
• PhotoResizeD100T.exe - overwrite the resolution information in the header without touching the pixels.
• PhotoResizeK20.exe - resize to approximate maximum size of 20kB.
• PhotoResizeG1024x768.exe - use content-aware resizing to change aspect ratio while preserving content.
• PhotoResizeA400x300.exe - crop and resize to 400x300 pixels. The central part is preserved and resized while the borders are cropped.
• PhotoResizeA400x300x5.exe - extend canvas and resize to 400x300 pixels. The last number (0-9) controls canvas brightness.

Additional options

• PhotoResize400R.exe - process recursivelly all sub-folders.
• PhotoResize400C.exe - place files to current folder (current folder can be specified in shortcut properties).
• PhotoResize400S.exe - skip files already smaller than the requested size.
• PhotoResize400O.exe - do not wait for Enter.
• PhotoResize400U.exe - skip files already existing in the destination location.
• PhotoResize400N.exe - sharpen image.
• PhotoResize400I.exe - overwrite source files.
• PhotoResize400M.exe - copy metadata.
• PhotoResize400E.exe - preserve file modification time in addition to file creation time.
• PhotoResize400A.exe - use arithmetic compression.
• PhotoResize400V.exe - auto-rotate be EXIF tag.
• PhotoResize400X.exe - process landscape (width >= height) pictures only.
• PhotoResize400Y.exe - process portrait (width < height) pictures only.
• PhotoResize400Q50.exe - set compression quality to 50%.