I have discovered a very easy way to resize a bunch of pictures using Linux.
First, you need to install imagemagick:
[CODE] sudo apt-get install imagemagick [\CODE]
Then, what I did was to copy all the pictures I wanted to resize into a temporay folder.
Finally, using the command line, I went to the previous folder, and typed the following:
[CODE] mogrify -resize 800x600 *.jpg [\CODE]
and all the pictures were resized.
Of course, you can choose any size you want. Instead of"mogrify", you can use "convert" which does not replace the picture but instead creates a new one with the desired size.
You can also rotate pictures. For instance:
[CODE] mogrify -rotate 90 picture.jpg [/CODE]
where "90" is the number of degrees you wish to rotate picture.jpg.
Here is a link with more infos on imagemagick: