Hi, and thank you for your question.
Picasa only offers the option to save images in JPEG format. However, if you want to convert the saved JPEG images to TIFF, please do this:
Right-click on the JPEG file saved on your computer, and click EDIT.
This will open up the image in MS Paint; from there, click on the blue File menu at the top-left corner, and click Save As > Other Formats.
Next, set "Save as Type:" to TIFF, and then save the file accordingly.
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