If you modify an image in Picasa (changing the contrast, effects, and so on), your edits are only visible when the image is viewed in Picasa. The program never alters your original pictures; it merely makes note of the changes you've made. While this ensures that you don't inadvertently alter your original photos, it can make things difficult if you want to share the pictures with others (who may use a different program for editing and viewing images) or if you want to do additional editing in another program.
To simplify the process of sharing your pictures, opening them in other programs or on other platforms, and backing them up for safekeeping, Picasa provides four procedures. See the table below for a quick summary of the purposes and differences between them. We'll discuss each of these procedures in depth.