If you want to heart an image that is on the site, just move your mouse over the image and click on the heart icon.
On the image page you can find the heart icon next to the image title.
When you click the heart icon it will fill up, indicating that you've hearted that image.
On your heart page, you can see all the images you've hearted. If you move your mouse over the image you'll see the heart icon. Click on it and it will get outlined, indicating that you've un-hearted that image.
Hearting images from other sites
If you want to heart images from other sites you'll need our Heart-Button. This tool allow you to easily send the images from any site to your profile.