You didn't give an example of the URL you replace the "the URL of your image" String with, which makes it difficult to determine why it didn't work.
URLs can be devided into two main categories:
A. Relative.
These URLs are used to reference an external media file that is being stored in a location that is relative to the location of the HTML file that wants to access it.
Ex 1: If you had a local folder & file structure like the following, into which you have saved the HTML file (adventure.html) you generated via the Twine 2.x application's Publish to File option.
C:\adventure
adventure.html
\images
forest.png
desert.png
... then to show the forest.png image you would use a Relative URL like the following.
<img src="images/forest.png" width="500" height="300" alt="Forest">
Ex 2: If the web-server you are hosting the above adventure.html file on has a folder & file structure like the following
www.mysite.com
adventure.html
\images
forest.png
desert.png
...then you could use the same Relative URL as the above Ex 1 to reference the forest.png image.
B. Absolute.
These URLs are used to reference an external media file that is being stored in a location that is not relative to the location of the HTML file that wants to access it. This other location is likely to be an external web-server or file-server.
Ex 3. If you are using the Twine 2.x application's Test or Play options to view your story, and the images are being hosted on a web-server with the following folder & file structure.
www.mysite.com
\images
forest.png
desert.png
... then to show the forest.png image you would use an Absolute URL like the following.
<img src="http://www.mysite.com/images/forest.png" width="500" height="300" alt="Forest">
Ex 4.If the (published) adventure.html file was being hosted on one web-server (like philome.la) and the external images were being hosted on a different web-server or file-server (like www.mysite.com), then the Absolute URL you would use to show the forest.png image would look the same as that in Ex 3.