Add directory to install to qmake project file:

target.path = /opt/myapp
images.files = images
images.path = /opt/myapp
INSTALLS += target images

When the deployment method is using rsync, it will copy the contents of images directory into /opt/myapp. This is different from make install which will copy the images directory itself to /opt/myapp.

Remote deployment with rsync results in:
/opt/myapp/image1.jpg
/opt/myapp/image2.jpg
/opt/myapp/subdir/image3.jpg

But make install results in:
/opt/myapp/images/image1.jpg
/opt/myapp/images/image2.jpg
/opt/myapp/images/subdir/image3.jpg