Resize Images Online - Maintaining Quality
To select a portion of the image use crop when logged in. When the option is available (depending on aspect ratio) you will be able to crop the middle of the image automatically even if not logged in using center-crop
Smoothing and Reducing Noise
By default a very low level of smoothing is applied on soft parts of the image. This can be disabled only in the desktop application.
If you have a noisy photo use denoise. For a degraded or low resolution image use strong smoothing.
On free accounts the image is enlarged to maximum 200% (2 times) the original/cropped size. Any picture below 800x600 can be resized to this resolution if it doesn't require more than 600% zoom.
Vote, make private/public, delete an image
Use the icons in the actions pane to vote up or down for the image. If it's your own picture use the icons to make it private/public or delete it.
High quality resizing
To enable higher resolutions and lift the 200% zoom limit you need to create a Premium account. For this you need to have at least 1 credit available. Buy credits here.