necessary for a specific purpose for example to highlight a specific point in an argument such editing may include for example av selection and annotation zooming in and out cropping picture enhancement noise reduction slow motion playback pausing split screen comparisons etc although it will be appreciated that many more operations may be made available the recipient 40 b is therefore provided with a verified preparation tool vpt 302 the vpt 302 is an application either software hardware or a combination of both that has been designed to provide resistance to malicious attacks the vpt 302 has a rendering and editing component not shown that the recipient 40 b uses to perform the various editing rendering operations mentioned above the recipient 40 b can therefore prepare av evidence for later use preferably the vpt 302 permits real time rendering of the evidence copy 38 b according to the edit decisions made by the recipient 40 b the vpt 302 also has an edit decision list generation component not shown once the recipient 40 b has finalised the edit decisions required on the evidence copy 38 b the edit decision list generation component of the vpt 302 generates an evidence presentation list epl 304 the epl 304 contains details about all of the edit instructions required by the recipient 40 b the epl 304 may contain one or more groups of edit instructions each group containing one or more edit instructions that are intended to be performed sequentially for example the epl 304 may consist of the following data play av from start timecode 01 00 20 13 to end timecode 01 00 22 02 play av from start time code 01 00 22 03 to end timecode 01 00.