how to compress files

If you right click a picture and choose "Send to" you can select evolution to email somone, and further options in the window allow you to compress the file also before emailing.

Choose .zip compression for maximum compatibility.

Thank you.
I've tried.
It should work.
However, compression is not enought.
Do you know if there is any way to compress quickly pictures from 1 Mo to 80 - 200 Ko transforming them as light jpg files ?

You could resize them?

There is a program called "convert" which is part of a package called imagemagick. It can be run on the command line and in batch can convert images from one size to another.

If you install imagemagick from synaptic package manager (in System --> Administration) you can then in a terminal (Applications --> Accessories --> Terminal) and use something like they outline here:-

http://www.imagemagick.org/script/convert.php

Alternatively there is a tool called mogrify which can do this. There are quite a few how-tos around if you google for "resize and convert" or "resize and mogrify"