Running external programs: what is the best way?

[sir_alex]

If i have to execute an external program (for example, in the frontend
that i created for convert, from ImageMagick) i have 2 possibilities: i
can call one function between the exec* family, or i can call the
system function: so, which in your opinion is the best? The only
difference that i know (but i may be in error) between these 2
functions is that the former doesn't return (so you have to create a
child process), but the latter returns. Is this the only difference?