pass arg to node not working

edit

roslaunch pure_vision pure_vision_single_image.launch arg1:="ct.jpg" why is this not working?

Because with arg1:= instruction you are passing ar argument to the launch file not to the node, for this, as I said, you will need to add and argument to the launch file.

so what is the exact launch file and exact command to pass an image to the node in that launch file? i'm kind of confused.

I have edited the answer to be more clear. You just need to add and argument to the launch file.

Have you tested this way yourslef? cas still its not working for mine.

Well, I did not test it with the pute_vision package since I assume that is your own pakage and I am not able to clone it in particular. But I tested the launch file and command in one of my own packages and it works perfectly.

Also I assummed that you have programmed properly the fact of storing the parameters passed to the node since the first command (rosrun pure_vision my_publisher bird.jpg) you mentioned works for you.

int main(int argc, char **argv)
{
...
ROS_INFO("Passed arg to %s is %s", argv[0], argv[1]);
...
}

If the problem persist you can post here code chunks to start debuggin what is going on.