If you follow the steps I posted on the other page, particularly #7, then it should work ok for you.
1: Click on the image
2: Select 'Edit'
3: Click on 'Adjustment'
4: Click on 'Resize'
5: If the picture is in Landscape format, in the 'Width' box overwrite what is there with "640". If the picture is in Portrait format, in the 'Height' box overwrite what is in there with "480". If the number in the appropriate box is less than these figures, then ignore what I have just said. Also, make sure that the box marked 'Keep Proportions' is checked.
6: Click on 'Apply'
7: Click on 'Save as Copy' and use the copy to post the image.