Featured image slider

Hi there. I haven't updated my blog for a long time but I'm getting back into it now. Back when I stopped working on it everything was fine, but now the featured image slider pictures are distorted. They are the same pictures as back when they were working fine. I checked them all and they are all 1600x600 as they are supposed to be. I tried re-uploading them but it didn't work. The weird thing is that the first (out of 3 pictures) is showing normally, but the 2 others are stretched downward, but not to the sides, for some reason. I also tried cropping one of the warped pictures and even though it was cropped to a smaller size than 1600x600 it still showed up larger than the first pictured that had retained its correct size. I'm clueless about what the problem is and how to fix it. I hope you have a solution. Thank you!