There is a free photo editing software that I use called Gimp - It is easy to use and to scale the images you go to menu bar at top click in image then find scale image on the drop down menu. Enter around 1000 in the top entry box, the rest will be looked after automatically when you click on OK.

Export the photo as a .jpg format and it is ready to load onto ebay. Its been working for me since I started revising all my photos to comply.

Gimp also has easy to use colour, cropping, correction tools.

Not as good as photoshop, but still excellent and FREE