This is an OS X command-line script that downloads the latest DSCOVR:EPIC <http://epic.gsfc.nasa.gov/> image and sets it as your desktop picture. Prerequisites: requires installing Homebrew <http://brew.sh/> and then the jshon tool (`brew install jshon`). Then you can run the command manually, or add it to your crontab.

dscovr-epic-desktop

#!/usr/bin/env bash
download_directory="$HOME/Desktop/_dl/epic-earth";
apiurl="http://epic.gsfc.nasa.gov/api/images.php";
curl -s "$apiurl" | jshon -a -e image -u | while read image; do
    destfile="$download_directory/$image.jpg";
    mkdir -p "$download_directory";
    if [[ -n "$image" && ! -f "$destfile" ]]; then
        echo "New 🌍 ! $image.jpg";
        curl -so "$destfile" "http://epic.gsfc.nasa.gov/epic-archive/jpg/$image.jpg";
        ln -sf "$destfile" "$download_directory/latest.jpg";
    fi
done
latestfile=$(readlink -f "$download_directory/latest.jpg");
if [[ -e "$latestfile" && $(stat -c '%Y' "$latestfile") -gt $(($(date +'%s') - 60)) ]]; then
    # If latest file exists, and it's last modification time less than than 1 minute, set it to desktop.
    osascript -e "tell application \"Finder\" to set desktop picture to POSIX file \"$latestfile\"";
    killall Dock;
fi

#####################################################################
# EPIC Daily “Blue Marble” API documentation:
#####################################################################
#  The API URL is:
#  http://epic.gsfc.nasa.gov/api/images.php
#
#  This gets you a list of the latest day’s images & metadata.
#
#  OR
#
#  http://epic.gsfc.nasa.gov/api/images.php?date=YYYY-M-D&w=X&e=Y
#
#  The second form’s optional parameters allow you to focus in to
#  geographical regions that were in view (technically, longitudinal
#  bounding points) on a given date.
#
#  For instance: Using North America’s boundaries of east =
#  -53.034, and west = -170.859 and choosing August 24, 2015, the URL
#  would look like this:
#
#  http://epic.gsfc.nasa.gov/api/images.php?date=2015-8-24&w=--170.859&e=-53.034
#
#  The date parameter is unpadded(e.g. 2015-9-1, vs. 2015-09-01 for
#  September 1, 2015), and optional. Leaving the date off will default to
#  the latest image set.
#
#  Leaving out the coordinates gets you every image for whatever date is
#  returned.
#  Adding either longitudinal parameter returns all images for the given
#  date, for which the supplied longitude is in view of the camera.
#
#  The JSON data looks like this:
#
#  ImageData object:
#
#  {
#  "image": "epic_1b_20150826231708_00", // image name sans extension.
#  "caption": "About an image", // Will contain a caption
#  "coords": “{}", // Contains a JSON string representing a
#  Coordinates object.
#  "date": "2015-08-26 23:17:08" // The date the capture sequence for the
#  data was initiated
#  }
#
#  ImageData notes:
#
#  For the image field to be useful, it has to be added to a URL. Image
#  URLs differ depending upon purpose.
#
#  Given an image name of “epic_1b_20150901205648_00” (taken
#  Sept 1, 2015, with the camera aimed
#  at 3 storms in the pacific (my favorite)), we have URLs as follows:
#
#  For compressed JPG thumbnails, the URL would be:
#
#  http://epic.gsfc.nasa.gov/epic-archive/thumbs/epic_1b_20150901205648_00.jpg
#
#  For full-size, compressed JPG previews, the URL would be:
#
#  http://epic.gsfc.nasa.gov/epic-archive/jpg/epic_1b_20150901205648_00.jpg
#
#  For full-size original PNG images with full metadata in the comments,
#  the URL would be:
#
#  http://epic.gsfc.nasa.gov/epic-archive/png/epic_1b_20150901205648_00.png
#
#  Coordinates object
#
#  {
#  "centroid_coordinates": { // Geographical coordinates that the
#  satellite is looking at
#  "lat": 4.076132,
#  "lon": -169.648562
#  },
#  "dscovr_j2000_position": { // Position of the satellite in space
#  "x": -1439710.750000,
#  "y": 659227.437500,
#  "z": 113316.414062
#  },
#  "lunar_j2000_position": { // Position of the moon in space
#  "x": 153199.062500,
#  "y": -319797.531250,
#  "z": -104905.093750
#  },
#  "sun_j2000_position": { // Position of the sun in space
#  "x": -134918656.000000,
#  "y": 62555808.000000,
#  "z": 27119770.000000
#  },
#  "attitude_quaternions": { // Satellite attitude
#  "q0": 0.976360,
#  "q1": -0.212080,
#  "q2": -0.039540,
#  "q3": 0.013750
#  }
#  }