Standardise Image Size

Hi.
Was hoping to change my site to this template as I love the simple design and use of photographs. We are a catering company and so a picture can save a thousand words.
I have been playing with the live preview and noticed when we use our images they are all different sizes. Is there a process and a widget you would suggest to get the images the same size and resolution??

Many thanks

Great theme!!

Regards

Carl