The number of international Web sites showing sexual abuse of children has fallen by about 10 percent, but the images on these sites are more violent, a British Internet watchdog said Wednesday. The Internet Watch Foundation said increased vigilance by UK police and private groups that operate a series of hot lines has made it harder for commercial groups to operate child pornography Web sites. Illegal sites are often removed within hours, the group said. But those that remain online are more likely to use images involving torture and penetration, the report said. These types of graphic images were found in 58 percent of child pornography sites, compared to 47 percent two years ago. The report also found that 24 percent of the children used in the photographs and videos appear to be 6 years old or younger.