The logo that appears on all pages is put there by the LOGO skin object. If you want to remove that from one page and add your own image, one way to do it is:
- Copy and rename the skin file and it's corresponding doctype file.
- Edit the file to replace the LOGO skin object with an image tag that refers to the image that you want to use.
- Apply the new skin to the page.
That's is the bare-bones description. If you'd like some more detail, do let me know and I'll add some details.
DotNetNuke doesn't have a facility for a "page logo" or something like that.
The other way to do this would be to replace the skin object with a content pane into which you can place an HTML module that contains an image. Set the module to display on all pages. Remove it from pages where you want a unique image, and put a unique module there.