While writing a scientific paper on tag recommendation I checked – just out of curiosity – the share of images tagged by their uploaders on Flickr. I found out that 4 out of five images are untagged and that less than 15% of images have 2 or more tags.

My method and detailed results: In general one would need a random sample for such an investigation, but a truly random sample is hard to obtain without access to the data base. Therefore I just grabbed 20,004 images from the RSS feed for recent uploads and counted the number of tagged images. Easy enough I also computed the confidence interval:

• In my sample 3,650 images were tagged with at least one tag, that makes p1=18.25%
• With alpha=0.99 p1 is in [16.84, 19.66].
• That leaves more than 4 out of 5 images untagged.
• Also in my sample 2,628 images were tagged with at least two tags, that makes p2=13,14%
• With alpha=0.99 p2 is in [11.9, 14.37].
• That means that less than 15% of the images images have more than one tag.