ffmpeg -f v4l2 -i /dev/video0 -ss 1 -vframes 1 -qscale:v 2 o

$ vlc v4l2:///dev/video0
VLC media player 2.1.2 Rincewind (revision 2.1.2-0-ga4c4876)
[0x9ba148] main libvlc: Running vlc with the default interface. Use 'cvlc' to use vlc without interface.

(vlc:24750): Gtk-WARNING **: Unable to locate theme engine in module_path: "murrine",

(vlc:24750): Gtk-WARNING **: Unable to locate theme engine in module_path: "murrine",

(vlc:24750): Gtk-WARNING **: Unable to locate theme engine in module_path: "murrine",
Fontconfig warning: FcPattern object size does not accept value "0"
Fontconfig warning: FcPattern object size does not accept value "0"
Fontconfig warning: FcPattern object size does not accept value "0"
Fontconfig warning: FcPattern object size does not accept value "0"
[0x7f4fd0001248] main vout display error: Failed to resize display
$ That displayed successfully!^C
$ sudo ffmpeg -f v4l2 -i /dev/video0 -ss 1 -vframes 1 -qscale:v 2 output.jpg
ffmpeg version 2.1.1 Copyright (c) 2000-2013 the FFmpeg developers
  built on Dec 10 2013 06:36:11 with gcc 4.8.2 (GCC)
  configuration: --prefix=/usr --disable-debug --disable-static --enable-avresample --enable-dxva2 --enable-fontconfig --enable-gnutls --enable-gpl --enable-libass --enable-libbluray --enable-libfreetype --enable-libgsm --enable-libmodplug --enable-libmp3lame --enable-libopencore_amrnb --enable-libopencore_amrwb --enable-libopenjpeg --enable-libopus --enable-libpulse --enable-librtmp --enable-libschroedinger --enable-libspeex --enable-libtheora --enable-libv4l2 --enable-libvorbis --enable-libvpx --enable-libx264 --enable-libxvid --enable-pic --enable-postproc --enable-runtime-cpudetect --enable-shared --enable-swresample --enable-vdpau --enable-version3 --enable-x11grab
  libavutil      52. 48.101 / 52. 48.101
  libavcodec     55. 39.101 / 55. 39.101
  libavformat    55. 19.104 / 55. 19.104
  libavdevice    55.  5.100 / 55.  5.100
  libavfilter     3. 90.100 /  3. 90.100
  libavresample   1.  1.  0 /  1.  1.  0
  libswscale      2.  5.101 /  2.  5.101
  libswresample   0. 17.104 /  0. 17.104
  libpostproc    52.  3.100 / 52.  3.100
Input #0, video4linux2,v4l2, from '/dev/video0':
  Duration: N/A, start: 260858.172031, bitrate: 48660 kb/s
    Stream #0:0: Video: rawvideo (YUY2 / 0x32595559), yuyv422, 352x288, 48660 kb/s, 30 fps, 30 tbr, 1000k tbn, 1000k tbc
[swscaler @ 0xc13ee0] deprecated pixel format used, make sure you did set range correctly
Output #0, image2, to 'output.jpg':
  Metadata:
    encoder         : Lavf55.19.104
    Stream #0:0: Video: mjpeg, yuvj422p, 352x288, q=2-31, 200 kb/s, 90k tbn, 30 tbc
Stream mapping:
  Stream #0:0 -> #0:0 (rawvideo -> mjpeg)
Press [q] to stop, [?] for help
[video4linux2,v4l2 @ 0xc1b5a0] The v4l2 frame is 79552 bytes, but 202752 bytes are expected
/dev/video0: Invalid data found when processing input
frame=    0 fps=0.0 q=0.0 Lsize=N/A time=00:00:00.00 bitrate=N/A
video:0kB audio:0kB subtitle:0 global headers:0kB muxing overhead -inf%
Output file is empty, nothing was encoded (check -ss / -t / -frames parameters if used)
[video4linux2,v4l2 @ 0xc1b5a0] Some buffers are still owned by the caller on close.
$ ls output.jpg
ls: cannot access output.jpg: No such file or directory