To use your new image style with an image field, first enable it for the field (Structure > Content types > [type name] > Manage fields > [field name] > Available image crop styles) and then ensure the Image style is selected on the appropriate Display.
Once an author with the appropriate imagecrop permissions has uploaded an image to a node, they will be shown a 'Crop image' button on the node edit page. Clicking the button will open a popup with a dropdown list of all the imagecrop styles available. The author then chooses the appropriate style, applies the desired cropping, scaling and other effects and clicks save. The crop settings are reused wherever the image is shown with the same style, so there is no need to repeatedly crop the same image.
The above instructions use Drupal 7 terminology. If you are using Drupal 6 and struggling to follow them then check the module's README.txt which is written specifically for Drupal 6.
Image (Drupal core field type)
User (Drupal core) for the profile picture
Media module 7.x-1.x and 7.x-2.x
If you'd like the module to support another type of image then please submit a patch in the issue queue.
image and Acidfree Albums : Link is underneath the thumbnail on the edit page.
Node Images : Underneath the thumbnail. You will need to add an override function to your theme's template.php; see README.txt for details.
After you enable the module, you can go to admin/settings/imagecrop and enable support for modules & fields to display a link.
Three screencasts are available:
http://www.screencast.com/users/timmillwood/folders/Jing/media/ef47425b-... : Drupal 6
http://realize.be/imagecrop-5x10-out : Drupal 5
http://realize.be/imagecache-2-and-imagecrop : Drupal 5 (early development)
More info is in the README.txt file.
Note: Drupal 7.20 and up require the dev version until 7.x-1.0-RC4 is released. If you want to help get 7.x-1.0-RC4 released, see the meta issue.