I wrote this macro to display images in my book. It should place the image to the left, filling ~50% of \textwidth, then the caption is to the right.

\setupcaption[location=right, minwidth=.5\textwidth]
\define[4]\figureis{%
    \placefigure{#2, Courtesy #3, photo no. #1\nocite[#4]{}}{\externalfigure[#1][maxheight=.7\paperheight, maxwidth=.5\paperwidth, minwidth=.5\paperwidth]}
}

#1 = filename, other variables are used for reference/credit details.

The problem is, somehow some images are inexplicably displayed very tiny on the page. I check the image file and they are not small, but somehow is rendered small with the code above.

What is wrong in my code?

--Joel