Save your camera files into a "safe" folder. Do not ever manipulate these files.
When you want a smaller file to email, make a copy of the photos into a new folder and use Irfanview to batch re-size them. This will give you smaller files to email without losing data on your original files.
An alternative is to convert all your camera files immediately to TIFF format and save them. TIFFs are lossless - they don't dump data with each save. So, you can then use those master files and resize, etc., then save as to a jpeg. When changing the format from TIFF to jpg, you should be required to do a save as, so you don't risk saving over your original file and losing data. TIFFs will be bigger than a jpg file because it never dumps data it thinks you don't want. Jpgs dump data with every save - it's like photocopying a photocopy, with every copy, the image degrades.
1975 American Clipper RV with Dodge 360 (photo in profile)
1998 American Clipper Fold n Roll Folding Trailer
Both born in Morgan Hill, CA to Irv Perch (Daddy of the Aristocrat trailers)
