Get Post Image allows you to easily get and convert an image from a post, it supports resizing, color corrections, masks and other advanced operations
For example, to display a post thumbnail in a 200x100 format, you can simply do:
Or as a shortcode in the post content:
If the picture is a little bit dark, you can increase brightness in 20% with:
And the shortcode:
There's many more options. Please visit the plugin page for configuration, usage, examples and other information.