Leave out auxiliary verbs
With perfect, progressive and passive structures, auxiliary verbs are not necessary. This makes some headlines appear to be in the past tense, when actually the headlines use past participles, or particles, not the past simple. Similarly, changing events are represented by the present participle on its own.
New policy decided by Parliament (New policy has been decided by Parliament)
Lion escapes zoo – ten killed (ten people have been killed / were killed)
Four stranded in sudden flood (four people have been stranded / were stranded)
Temperatures rising as climate changes (temperatures are rising)