try the custom webviewer
usually the web component is used to connect to a MySQL database, see also App Inventor Tutorials and Examples: MySQL | Pura Vida Apps and to upload files, the most simple method is to use ftp... there are ftp extensions around, for example this one App Inventor Extensions: FTP | Pura Vida Apps
however the web component does not offer multipart/form-data, which your script is using...
the custom webviewer mifght be able to pick and upload an image to your server...
see this exanple CustomWebView Camera permission - #10 by Patryk_F about how to get required permissions
Taifun