NASA's Image Detective Tutorial

Photos taken with the 50mm are normally easier to locate because they cover a larger area of the Earth and often include recognizable geographic features. Photos taken with longer focal length lenses like the 180mm, 400mm and 800mm lenses are progressively more difficult to locate due to the fact that the area covered is progressively smaller and smaller while the features in the images appear progressively larger.

Images taken that look straight down from the Space Station at the Earth are called nadir images. Images taken at differing angles from nadir are more difficult to locate as the land toward the edges of the images appears foreshortened. These off-nadir angles are called oblique angles and the corresponding images are known as oblique images. In addition, the angle at which features appear in such an image could appear differently than when viewing the same feature in Google Earth/Maps or in Bing Maps. This could make it more difficult to place a center point. In such a case, the area in the image may be a significant distance away from the spacecraft sub-orbital point.

After selecting an image, the map is zoomed and positioned such that the nadir position (latitude/longitude) of the spacecraft, when the image was taken, is in the center of the screen. This is not the same as the center of the image. The image can contain an area in any direction surrounding that nadir point.

Finding the center point of an image is sometimes easy if a feature is obvious - like with a round lake, a city center, or a river mouth. Simply drag the center of the image over the point on the map; no rotation is needed. More often than not though, the image will not contain an obvious feature to match up with the map, and you will need to use the zoom and rotate tools for an approximate fit of the image to the map to find the center point. This will help you to be sure the subtle image features you're seeing are really those on the map. Remember also that astronaut images almost never have north at the top of the image (there is no up nor down in space!).

Click the circular clockwise and counterclockwise arrow buttons in the Image Controls panel to rotate the image. The "Rotation" box will display the current rotation value in degrees of the image from its initial display orientation. You can choose rotations in 1, 5 or 45 degree increments.

On the Image Controls make sure the box labeled "Mark center point after rotation" is checked before you select "Rotate", otherwise you will not have cross-hairs to center up the image over its corresponding location on the map. The cross-hairs appear as yellow vertical and horizontal line crossing the center of the image.

Use the "Grow" and "Shrink" buttons in the Image Controls or the mouse wheel to resize the image to fit the size of the map. Conversely, you can use the map controls to zoom in and out on the map to fit the size of the image. You can click and drag the image to reposition it over the map or you can use the north, south, east and west pan controls to slide the map beneath the image. You can also simply drag the map around to pan it. Resize and move the image relative to the map until the features in each overlap or overlap as much as possible. The features do not need to match exactly; the only thing that will count towards your points is that the center point lines up exactly.

When you click and drag the image, it will become partially transparent so you can better view the map underneath to align the features to those on the map. You may also use the "Hide" and "Show" buttons in the Image Controls as needed. Note that even though the image scale looks correct in one area of the photo, it may look too small or large in other areas of the photo. This is due to the image being photographed off-nadir, making it oblique. In such case, you will not be able to get all of the features to overlap, so do the best you can in getting as much of the image and the map to overlap.

List features that you can actually see in the image. The feature may appear anywhere on the image, not just at the center point. You may add more than one feature. If you enter more than one feature at a time, separate them with commas including a space behind the comma, like this: Catskill Mountains, Hudson River, Albany Intl Airport.

When you pass the tutorial and start locating imagery, you login by using your badge number, or your Detective ID and Secret Passcode. Image Detective IDs will generally be checked and accepted within about 24 hours after submission.

When placing images, you will be awarded points based on the focal length of the camera lens. Images taken with higher focal length lenses are worth more points because they are usually harder to identify. Extra points are awarded for specifying features - such as airports and lakes. In order to get the maximum amount of points possible for one submitted image, you should first identify the center point correctly, add cloud cover percentage, and identify features in the "Feature(s)" field. The longer the image is left in the database without being geolocated, the more points that image will be worth.

Your points will be posted as the images are added to the NASA imagery database, which normally takes a few days.