Hello,
There are several ways to display an image in custom size.
1) The simplest would be to use the width and height parameters with the image field. These were not in the documentation, so I’ll update it. It’s also recommended to set the size parameter with the closest size and the same proportion.
[field image="field_name" size="thumbnail" width="50" height="50"]
2) If you want to use this custom size for many images on the site, it would be more efficient to change the default size under Settings -> Media. For example, you can set all thumbnails to be 50×50.
The new size will apply to all images uploaded after the change. You can use a Regenerate Thumbnails plugin to resize existing images. After the change, you can just use the default name of the size:
[field image="field_name" size="thumbnail"]
3) Another way is to register a custom size in the theme’s functions.php file.
add_image_size( 'homepage-thumb', 50, 50, true ); // (cropped)
Then you can use this registered name in the size parameter:
[field image="field_name" size="homepage-thumb"]
This method is not so recommended because you’ll have multiple versions of all uploaded images, one for each size. So, unless you plan to use more than 3 different sizes, it’s better to change default sizes in the site settings.
