Solution #1 Manual editing pictures
try editing the picture with photoshop or gimp(freeware). When you transform them into png and make the white background transparent and then optimize the hight/width of the picture you might get the solutiont you need.
Search for youtube tutorials
Solution #2 Use CSS to display the pictures in a different way
you could also show your pictures in your website in a way, that you set the hight/width of the pictures with CSS.
Adding a vertical-align you might also get to a different solution without editing the images yourself which might look different, but it should also fit your purpose.