You might have forgotten to upload the individual image files along with the .html page...
...or, you've possibly uploaded them to the wrong location...
...or you could have a case structure problem. Servers are CaSe SenSitiVe, so a link to IMAGES/image.jpg will not go to a file called images/image.jpg (they're two separate locations on most servers).
As Ben hints, it's all guesswork without a link to your uploaded page. Could you post one?