Free versions of Fotosizer and paint.net are both pretty east to use and rather clean for free apps. These are both quick and painless way to 'optimize' for the interwebz.
Reshade is a much better image resizer but is more complex. Biggest downfall to the trail version is that it is once use only. Close it and your free trial is over. Solution to that is to reinstall it every time you need to use it and then clean up the registry errors with something like the free AVG PC tuneup.
Make a copy of the originals,
Work on the copies
"Save as" for the finished image.
Don't save changes on the copy of the originals.
(if you want heavy duty stuff, look into Genuine Fractals)
I don't believe we can resist the things which make no sense - I believe.