Product pic - resizing while maintaining background color

Hi there,

I have a bunch of product images with the dimensions:
Height: 3888 px.
Width 2592 px.

I need the images to fill a 600 x 600px square.
If the image height is reduced to 600px the width becomes 400px and therefore do not completely fills the square leaving a 'blank' piece on each side of the image.

What's the easiest way to do resize the image WHILE maintaining the image background color on both sides of the image? I can't believe that there isn't an easier way than using the clone tool to clone the background - which takes a while when you have 100+ images. I also tried the spot healing brush which just paints the product and not the background.

Photoshop user.
Example image attached.

If the image height is reduced to 600px the width becomes 400px and therefore do not completely fills the square leaving a 'blank' piece on each side of the image. Don't you need to keep the proportion? You may easily alter "Image size" from photoshop by setting the exact values required in the width and height fields. You may even record an "Action" in it and play the same on all files.

Yes - that's correct - but look at the example pic above - if I do not keep the proportion the image will look totally strange and stretched. That's what I want to avoid.