Downstream likely won't accept video/x-raw and the caps query
will return EMPTY caps. Instead, create a copy of the caps that
has all structure names replaced by 'image/jpeg'
Simple pipeline that shows the problem:
gst-launch-1.0 videotestsrc num-buffers=1 ! "video/x-raw, \
width=(int)640, height=(int)480" ! videoscale ! jpegenc ! \
"image/jpeg, width=(int)800, height=(int)600" ! filesink \
location=/tmp/image.jpg
db74901b6a