I had done this in V4, but V5 is a bit different.
First, find your image and save it to your PC - it doesn't need to be on the server.
Login to APEX as the developer, and select the Application, then select 'Shared Components':
Select the 'Static Application Files' under the 'Files' section:
The file will be uploaded - make a note of the reference, because that's how you'll tell your application where to find it:
Navigate to the Application Builder page, and select the 'Login' page (usually 101) to edit it:
Click on the 'Login' under regions to edit the region, and scroll down to the 'Attributes' section:
In the 'Region Image' item, this is where you put the reference that was shown after you uploaded the image : #APP_IMAGES#charts.jpg
Click on 'Apply Changes' to save it.
OK, now we have the image uploaded and referenced in the region, run the page to see it:
Whoa, that's not what I expected - the image was quite large, and it defaults to the original size.
Go back to the "Attributes" section of the region and resize it:
Click on 'Apply Changes' to save it, then run it again:
You can fiddle around with the settings to re-position it on the page, for example create a new region above it and put the logo / image there.