You can resize photos in KeepandShare at any time once they have been inserted into a photo blog or document.
To resize simply click on the photo and "handles" will appear at the edges and corners:

A normal photo that has not been selected
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Click on the photo and resize handles appear
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Once you grab a handle by pressing down with the mouse button on it (but not letting up), the photo will resize in real time as you drag the mouse around:

When you like the new size of the photo, simply release the mouse button and the resize operation completes.
Mac Users: the MacIntosh 'Safari' browser does not support the handles resize feature. However, the Mac Firefox browser on the Mac works great with photo resizing.