WPBeginner has an excellent tutorial that describes how to use the built in functions of WordPress to generate additional image sizes for use in themes. This is possibly a better alternative than using TimThumb.
Category: WordPress
Using WordPress To Create Multiple Image Sizes
1
Definitely better than TimThumb. I’ve used this method for a bunch of client projects over the past few months and I won’t go back. Really powerful and really simple — you just declare a size with add_image_size and then insert it wherever with the_post_thumbnail. (And yet so many ThemeForest themes still tell you to upload files with specific dimensions.)