While you can only open one file at a time for viewing or editing, many Picasa procedures work with multiple images. Most of the multi-image selection techniques described below can be used in combination with one another.
Select a single image by clicking its thumbnail, placing the image in the Picture Tray. If you click another thumbnail, it replaces the one in the Picture Tray.
Select any contiguous group of images in a folder or label by -clicking the first and last thumbnails in the group or by dragging a selection rectangle around the group.
Select non-contiguous images in a folder or label by -clicking each one.
Select starred images in the current folder or label by clicking the Starred text beneath the folder/label name or by choosing Edit > Select Starred.
Select every image in a folder or label other than the currently selected ones (inverting the selection) by choosing Edit > Invert Selection ().
Select all images in the current folder or label by clicking the All text beneath the folder/label name or by choosing Edit > Select All ().
Combine multiple selections by clicking the Hold button beside the Picture Tray after adding each group. When you click Hold, images currently in the Picture Tray are marked with a green target symbol. You can then freely add other images without worrying about the current ones being cleared. You must use this technique to select images from multiple folders.
To deselect all selected images in the current folder or label, click the None text beneath the folder/label, click a blank area in the Lightbox, or choose Edit > Clear Selection (). To clear all images from the Picture Tray, click the Clear button and click Yes in the Confirm dialog box that appears.