Methods and nodes (300a, 300b, 302) for handling a usage policy (P1.P2) pertaining to source data (D1,D2) generated by a source node (300a, 300b). The usage policy dictates permission to access and use the source data. The source node calculates a signature (Sig) based on an identification (id_D) of the source data and the usage policy (P) of the source data, and provides the source data, its usage policy and the calculated signature to a data processing node (302). The data processing node then generates new data (D3) based on the source data, and calculates a new signature (Sig3) based on an identification (ldj_)3) of the new data and at least one of: a new usage policy (P3) pertaining to the generated new data, and the usage policy (P1, P2) of the source data. The data processing node finally provides the new data, the usage policies (P1, P2, P3) and the signatures (Sig1, Sig2, Sig3) to a data receiving node (304) which is thereby enabled to verify and comply with the provided usage policies based on the respective associated signatures.