Initialize time stamp for published image messages (#475)

Use the current ROS time instead of leaving it unset.

Signed-off-by: Jacob Perron <jacob@openrobotics.org>

image_tools/src/cam2image.cpp

@@ -287,6 +287,7 @@ class Cam2Image : public rclcpp::Node
     msg.data.resize(size);
     memcpy(&msg.data[0], frame.data, size);
     msg.header.frame_id = frame_id_;
+    msg.header.stamp = this->now();
   }
 
   cv::VideoCapture cap;