> yes I know, but it could be a "placebo" :-P .. we are using the elog in a lan so it
> could be a good temporary solution ...
> 
> can you point me to some documentation I can read to be able to do it? should I edit
> the css file ?

No, I would have to add another option to the configuration file, it's not yet implemented. 

> can be usefull to be able to "optionally" execute some external program (a sort of
> pipe) in order to be (eventually) able to set a "filter program" for attachments.
> The same way an MTA does with procmail I mean.
> 
> in this case one has to be able to access both to the original image and the
> processed one...

Executing and external program is possible via the 

Execute new/edit/delete = ...

command. While you can pass attribute values to the program to be executed, it is not
possible right now to pass attachment names, although this could be easily added. What
would be harder is to reformat the whole entry. If you just downsample an image, that
would be ok. But if you want to keep the original, you would have to modify the logbook
entry to contain n*2 attachments afterwards, which would not be easy.

So I don't see a simple way of achieving what you want. Sorry.