Hi:
SAS will not "erase" any previously created external IMAGE files (such as those pointed to with an <IMG> tag). It may overwrite a previously created HTML file -- but if your SAS job created GCHART.PNG the first time you ran the code, and then you did a tweak or two and then ran the code again, the second time, SAS would create GCHART1.PNG; and if you did more tweaks, and resubmitted your code, then SAS would create GCHART2.PNG, etc, etc.
The -final- HTML file will contain an <IMG> tag that points to the name of the most recent file created by SAS/GRAPH. So if you are finally happy with your last run, (and that job created GCHART2.PNG), then you should find an <IMG> tag that points to GCHART2.PNG in your HTML file. However, the "older" images from your previous runs will still be out on disk -- they are external image files created for ODS HTML. If you want to have your storage "cleaned up" or these older files deleted, you will have to do the housekeeping yourself. (probably using an X command or a SYSTASK command -- since you have to delete operating system files.)
cynthia