Luckily I just saw this and can give you an answer.
If you have a copy of the image on your computer, the easiest way is to edit the label from the course page and replace the image manually. You would do all this in the text editor when you edit the label.
Apologies if I have misread the question, whichever way you are trying to do this, if don't have the correct url for the image, which may/or may not be on your server, your old code wont work, that is why I suggest that you basically reset each image tag by adding the image via the editor in your course summary or wherever.
At least that is what I think you do, I would do that if I were you. In doing this you might actually come accross your missing images when you see the file picker when adding the image, as you have an option to look for any image files on your system. As far as I know they will be in your Moodledata folder, but finding them is not easy as they are all encoaded with a very long filename made up of mainly numbers.
The file system for images has changed dramatically since Moodle 1.9 days.
You will find the Themes forum is helpful in things like images and such I am the Moderator there.