Your image(s) is placed in tomcat at path /img/image.jpg that is context relative path, the absolute path is /MyProject/img/image.jpg for your tomcat, eventhough it is /img/image.jpg outside of the apache. You proxy / -> /MyProject so when you add the context name to the path 'MyProject', it really doesn't work as you mentioned.
SOLUTION 1:
Use context relative paths in tomcat
img/image.jpg
In this case you have to be careful about the requrested URI, e.g. /MyProject/page1/action1/ has its image relative path
../../img/image.jsp
SOLUTION 2:
Use document root paths with leading slash
/img/image.jpg
and define the element base with the document root ('href' attribute). Just be careful about link!
<head>
<base href="http://www.mydomain.com/">
</head>
see http://www.w3schools.com/tags/tag_base.asp
SOLUTION 3:
Map the project to the same URI in apache as in tomcat (Personaly I use this solution as well because it is very easy, and I use a common word as a project/context name, e.g. 'web', 'site', etc.).
ProxyPass /MyProject ajp://localhost:8009/MyProject
SOLUTION 4:
Use a content filter such as mod_proxy_html http://httpd.apache.org/docs/current/mod/mod_proxy_html.html
NOTE: This solution is ever a bit slow (it doesn't matter witch filter you use)!
Be aware PROXY CONFIGURATION!!!
This is just about redirect etc., but you have a wrong configuration of your ProxyPathReverse!
ProxyPass / ajp://localhost:8009/MyProject
ProxyPassReverse /MyProject http://www.mydomain.com/
see the full explanation http://www.humboldt.co.uk/the-mystery-of-proxypassreverse/#more-131
read configuration examples http://www.apachetutor.org/admin/reverseproxies