If your image isn't the correct format, and let's face it, you never know what images people uploading you'll run the risk of badly cropped image.
If you have image of person that you've uploaded, but you need the image to appear landscape, you're in trouble.
Or let's say you have image, with person's face on the right hand side, but you need it to display in square thumbnail.
Regardless of the image format you upload, you can either use the automatic face detector or if you want even more control, you can add hotspots..
If you click 'Detect faces button, it will centre the crop using average of all the faces it finds..
You can click and create 1 or several hotspots to centre the crop of your thumbnails, if 'Detect faces doesn't work..
You can install the plugin using the tool from WordPress back-end..
This will crop the image to get as many hotspots in the thumbnail as possible or crop around the center of the hotspots if not...
My Eyes Are Up Here in the subject and the information.
Browse the code, check out SVN repository, or subscribe to the development log by RSS...
Read more