7. The method of claim 1 , further comprising: receiving a second digital image of at least a second portion of the unindexed document from the second user; extracting features from the second digital image; determining that the second digital image is similar to the first digital image based on comparing the extracted features from the first digital image to the extracted features from the second digital image; and strengthening an existing tie between the first user and the second user in the network based at least in part on determining that the second digital image is similar to the first digital image.
7. The method of claim 1 , further comprising: receiving a second digital image of at least a second portion of the unindexed document from the second user; extracting features from the second digital image; determining that the second digital image is similar to the first digital image based on comparing the extracted features from the first digital image to the extracted features from the second digital image; and strengthening an existing tie between the first user and the second user in the network based at least in part on determining that the second digital image is similar to the first digital image. 8. The method of claim 7 , further comprising comparing the extracted features from the first digital image to the extracted features from the second digital image based on a distance score generated from locations of the first user and the second user.