Methods and apparatus to identify media using hybrid hash keys

A computing system comprising:

• a processor;
• and
• at least one memory storing instructions that, when executed by the processor, cause the computing system to perform operations comprising:
• accessing a reference hash key in a reference database, wherein the reference hash key was generated based on a first portion of media;
• applying a blurring function to the reference hash key to generate a first blurred reference hash key, wherein the blurring function is configured to set at least one least-significant bit of the reference hash key to zero;
• comparing a metered hash key with blurred reference hash keys stored in a reference database, wherein the blurred reference hash keys include the first blurred reference hash key, and wherein the metered hash key is obtained from a meter device;
• and
• crediting the first portion of media with an exposure when the metered hash key matches the first blurred reference hash key stored in the reference database.

A non-transitory computer readable storage medium having stored thereon program instructions that, upon execution by a processor, cause performance of operations comprising:

• accessing a reference hash key in a reference database, wherein the reference hash key was generated based on a first portion of media;
• applying a blurring function to the reference hash key to generate a first blurred reference hash key, wherein the blurring function is configured to set at least one least-significant bit of the reference hash key to zero;
• comparing a metered hash key with blurred reference hash keys stored in a reference database, wherein the blurred reference hash keys include the first blurred reference hash key, and wherein the metered hash key is obtained from a meter device;
• and
• crediting the first portion of media with an exposure when the metered hash key matches the first blurred reference hash key stored in the reference database.