Rename Image in to company_logo.PNG while importing
if you are going to use a version under AnyConnect 3.0 such as 2.5 the name of the image should be company_logo.bmp
Then we upload it on the ASDM on the following path
Configuration > Remote Access VPN > Network (Client) Access > AnyConnect Customization/Localization > Resources.
Then you connect with the AnyConnect, disconnect, close it and reopen the AnyConnect.