These instructions are using Photoshop.
1. Go to File > Automate > Fit Image. Enter the correct number of pixels, which is 1600 width, 1200 height.
If you want to create a 'thumbnail' to accompany a print entry, rather than a DPI, go straight to step 3.
2. Any part of the frame not occupied by the image must be black or grey filled. So go to Image > Canvas Size. Set values to pixels. Alter the values so dimensions are 1600 width, 1200 height. Change canvas extension colour to black (it can be grey but black is the standard).
3. Convert profile to sRGB (recommended), using Edit > Convert To Profile and selecting sRGB from the drop-down. Alternative profiles, such as those used by commercial printers, may not project true colours.
4. Save the file as JPG. For a DPI entry, setting the quality at 10 or 11 will give a file size just less than 850KB (max file size for some external comps). For a 'thumbnail', a smaller file size is acceptable.
For submitting an entry to the monthly competitions SEE HERE