Changes

\setupexternalfigures [location=default] \definepageinjectionalternative [chapter:image] [renderingsetup=pageinjection:chapter:image]  \startsetups [pageinjection:chapter:image] \clip [width=\framedwidth,height=\framedheight] {\centerbox{% \externalfigure [\dummyparameter{name}] [%factor=, width=\structureuservariable{width}, height=\structureuservariable{height}, orientation=\structureuservariable{rotation}]% }} \stopsetups  \definepageinjection

\definepageinjection

[alternative=chapter:image, pagestate=stop]  \setuphead [chapter] [beforesection={\pageinjection[chapter:start]}, insidesection={\pageinjection[chapter:insert][namewidth=\structureuservariable{image}]}paperwidth]

\setuphead

% use if images are regularly numbered chap-cover-1, chap-cover-2, ...% insidesection={\pageinjection[chapter:insert][name={chap-cover-\namedheadnumberstructureuservariable{chapter}image}]}, insidesection={\pageinjectionsetuppageinjection[chapter:insert][namewidth={\structureuservariable{imagewidth}}]}, ]   \setuppagenumbering [alternative=doublesided]  \setupexternalfigures [location=default]  \starttext \startchapter [title={Mill}] [image=cow-black,rotation=90,width=\paperheight] \dorecurse{7}{\samplefile{lorem}} \stopchapter  \startchapter [title={Mill}] [image=cow-brown, rotation=-90,width=\paperheight] \dorecurse{11}{\samplefile{lorem}} \stopchapter

\startchapter [title={Mill}] [image=cow, rotation=-90,width=\paperheight] \dorecurse{7}{\samplefile{lorem}} \stopchapterstarttext

\startchapter [title={Mill}] [image=hacker, rotation=90cow,width=\paperheightpaperwidth] \dorecurse{7}{\samplefile{lorem}} \stopchapter

\startchapter [title={Mill}] [image=spider, rotation=-45,width=\paperwidth] \dorecurse{11}{\samplefile{lorem}} \stopchapter

\startchapter [title={Mill}] [image=mill, heightwidth=\paperheightpaperwidth] \dorecurse{7}{\samplefile{lorem}} \stopchapter \stoptext