MI5 is enhancing working procedures after accepting calls from the coroner at the inquests into the 7/7 London bombings, which killed 52 people.
Lady Justice Hallett had called for improved record-keeping and procedures for showing photographs to informants.
They were among nine recommendations she made for MI5, the emergency services and Transport for London.
MI5 said it had invested in a new IT system to allow higher-quality photographs to be sent to agents.
The agency had come under fire during the inquest for having cropped a clear colour photograph of plot ringleader Mohammad Siddique Khan so badly it could not be shown to an informant.
MI5 said it had used "wet film" in 2004 and a scanner but was now using better technology to avoid a repeat of the situation.
"This has improved the overall quality of the photographs we show to our agents."
However, it admitted the system was "not yet perfect".
The suicide bombers targeted Tube trains at Aldgate, Edgware Road and Russell Square and a double decker bus in Tavistock Square.
In concluding that the 52 victims had been unlawfully killed, Lady Hallett said delays in the emergency services' response had not caused their deaths.
Lapses
However, she criticised lapses by emergency services and MI5 and said she was making her recommendations with the aim of saving lives.
They included providing inter-agency training for front-line staff, new procedures to inform emergency services when power to Tube lines was off and better training for ambulance staff in dealing with large numbers of casualties.
Lady Hallett also said MI5 should examine its procedures to try to further improve the recording of decisions on the assessment of targets.
In its statement, MI5 said it had improved record-keeping and in 2008 set up a database of all requests made to show photographs to "agents reporting on international counter-terrorist targets".
Improvements to the database were being trialled to ensure there was a full record of which agents had seen which photographs, it said.
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