You use invoke-webrequest and it works fine with some websites. But sometimes you find that PowerShell says "command not found." What is wrong?
invoke-webrequest will work to download html and htm files. Depending on the source file on the web server, the command needs a flag to work properly. For an image file with a .jpeg extension, the invoke-webrequest needs a flag "-ContentType 'image/jpg'" or something similar to work. The flag depends on the file that you are downloading from a web server. This command below is an example of a non-HTML file that you want to download with PowerShell (the file happens to be an image file named foobar.jpeg).
invoke-webrequest http://source/URL/foobar.jpeg -ContentType 'image/jpg'
If you do not need to do type checking when it downloads, try a wildcard:
invoke-webrequest http://source/URL/foobar.jpeg -ContentType *