Including images in R package documentation file

Question

In fact, I have the same question than Teema Daniel Laajala, but the answer provided does not work for me.

The question was about displaying images in R package documention. When I write exactly the same code than in the ?par documentation file, which is :

\item{\code{mai}}{A numerical vector of the form \code{c(bottom,
    left, top, right)} which gives the margin size specified in
  inches.\cr
  \if{html}{\figure{mai.png}{options: width="35\%" alt="Figure: mai.png"}}
  \if{latex}{\figure{mai.pdf}{options: width=7cm}}
}

the image does not display and all I can see is : imagenotdisplayed.

Though, I did the exact same code as above, put my image in the folder figures in the folder man... So I was wondering If I was missing something, like a package I should install or something else...

Thanks for your help !