Adding different size image links in a slideshow

My website is based on a WordPress theme
I wish to include a number of images with links to other websites in a page but find that the images I have received are all of different sizes and aspect ratios, so I wonder if there is a widget or plugin which will let me display them as they are without the need to re-size or have them stretched or cropped. I guess the best way to do this would be in a slideshow, but the only ones I have found seem to require all of the images to be the same size or else they are stretched to fit or cropped.
Thanks in advance for any suggestions.