Automatic size or change background color of pictures?

Hi,

I’m starting to make my website and I have a problem with the background color of the pictures.

I changed the thumbnail and item size in JM Product Slider to show the pictures well with my camera proportion, but if I use another format, I can see the background white.

How can I change the white color for another different?

Can the frame be adjusted automatically to don’t show any color in the background?

I have the same problem when I go to the product page and I have the same questions.

I want the web without that white lines, I attach two pictures to show what I wanna remove.

Thank you very much in advance.