It is possible to automate a test which selects a file from your computer and upload it online? I tried to scan the windows of my computer which show when you click the upload button online but it seems it is not possible.
If I understand you correctly, you are scanning a website with upload functionality.
Just scan the upload button of the website. Most websites then show the operating system's "Open File" dialog. For automation you could simply paste the path in the "Open File" dialog and hit enter or click open.