I notice there isn't a standard size for pics on the site other than 300px wide.I think you might want to reconsider this and make it a standard size in height so you have consistent images. I think the 300x250 looks quite nice. That being sad, would you like the images re-sized/cropped, ect?
I take my pics and crop them ( the original size is like 2500 X 3500 or something crazy like that ) and that changes the aspect ratio. So when i resize i choose to select the width and it automatically changes the height to keep the ratio, thus they are all different. ( the cards i switched to 400 wide )I suppose its up to you. I can crop and resize or you can save me the time and do it for me 😀