A filter on both the client and server side should be implemented. For the server side, see UploadFile() in FileTransferHandler.ashx.cs; For a basic filter, read the headers["X-File-Name"] and filter on extension.
This would be in the Javascript templates, which are not part of this repo -- please direct your question to the jQueryFileUpload community.
HI i have 2 qus 1-how can change .net example to load only image files and if open another files like text show error and not load it
2-how can show image of file next the name هسفثشی خب یثبعمف (defualt state:for all file show "default_thumb.jpg"