title: ChildProcessError for image moderation firebase function
body: <p>I'm trying implement image moderation code to remove adult or violent content as given here: <a href="https://github.com/firebase/functions-samples/tree/master/generate-thumbnail" rel="nofollow noreferrer">https://github.com/firebase/functions-samples/tree/master/generate-thumbnail</a></p>
  
  <p>But every time i'm getting this error:</p>
  
  <pre><code>ChildProcessError: Command failed: convert /tmp/test folder/yes.jpg -channel RGBA -blur 0x8 /tmp/test folder/yes.jpg
  convert: unable to open image `/tmp/test': No such file or directory @ error/blob.c/OpenBlob/2712.
  convert: no decode delegate for this image format `' @ error/constitute.c/ReadImage/501.
  convert: unable to open image `folder/yes.jpg': No such file or directory @ error/blob.c/OpenBlob/2712.
  convert: unable to open image `/tmp/test': No such file or directory @ error/blob.c/OpenBlob/2712.
  convert: no decode delegate for this image format `' @ error/constitute.c/ReadImage/501.
  convert: no images defined `folder/yes.jpg' @ error/convert.c/ConvertImageCommand/3210.
   `convert /tmp/test folder/yes.jpg -channel RGBA -blur 0x8 /tmp/test folder/yes.jpg` (exited with error code 1)
      at callback (/user_code/node_modules/child-process-promise/lib/index.js:33:27)
      at ChildProcess.exithandler (child_process.js:213:5)
      at emitTwo (events.js:106:13)
      at ChildProcess.emit (events.js:191:7)
      at maybeClose (internal/child_process.js:877:16)
      at Process.ChildProcess._handle.onexit (internal/child_process.js:226:5)
  </code></pre>
  
  <p>due to this line:</p>
  
  <pre><code>// Blur the image using ImageMagick.
      return exec(`convert ${tempLocalFile} -channel RGBA -blur 0x8 ${tempLocalFile}`);
  </code></pre>
  
  <p>And one more help what is best way to moderate video instead of image, i.e. if i want to check if video uploaded is not offensive(adult or violent).</p>
  
  <p>Any help is appreciated.</p>