Inserting image into post with different image size

Question

I have a custom WordPress theme that I have made myself.

When I insert an image into a post I only get the option to add the full size image (see below screenshot):

In Settings > Media I have a number of different sizes defined. How come these options done appear when I'm inserting an image?

Answer 1

Have look at add_image_size and add to your theme's functions.php file:

http://codex.wordpress.org/Function_Reference/add_image_size

Answer 2

Just like gurudeb said but remember that you will have to either replicate thumbnails or re upload the images so that the thumbnails in your defined size can be created