send your content to dropbox, and you can import to istock. I go from my ftp server to dropbox then to istock.
There is a service that allows you to do ftp to dropbox and then to istock. I forgot the name. it is a service where you can take any input (ftp, www, http, dropbox, google drive, etc) and swap everything between each format. I forgot the name. it is expensive because you pay for data size, you save money if you have tens of thousands of transactions. I tried it and didn't like it. forgot the name.
the service is all icon driven. you drag the icons and put commands between the 2. so you drag an FTP icon and dropbox icon, link them, and type in a command, and it processes the command on all of your files. it is a web based service.