figure scaling

[Hans van der Meer <hansm@science.uva.nl>]

Typesetting a jpeg picture I found a small, but discernable error in  
the result.

\externalfigure[foto.jpg] 
[width=60mm,height=60mm,frame=on,rulethickness=.1pt]

I tried several pictures and all show that the picture extends above  
the topframe edge.
Using a thicker rule does not make the excess of picture disappear.
Either the picture raises above the topframe edge or, as well may be,  
the topframe edge is put somewhat to low.
I could determine which of these is the case.
The bottom edge and the left and right edges seem ok.

Did some examples, e.g.:
foto.jpg  scaled from 2592 x 1944 pixels down to 60mm x 60 mm
another one smaller of 340 x 510 pixels

It should be the scaling, because the picture comes out correct  
within the frame when typeset at its natural size.

Are there other people seeing this effect? Can it be corrected then?

yours sincerely,
dr. H. van der Meer