Obtaining people’s permission to use the photographs is ideal.
However, even if you don’t have a release, you can reduce your risk if you use:
(1) photographs from Stake/Ward histories (since those will hopefully already be covered by a release) or
(2) group pictures or pictures in which people are not easily identifiable.
If you submit photos, please sign the following release form linked to in the Stake/Ward history guidelines
The policies for “Use of Online Resources in Church Callings” (available here: https://www.churchofjesuschrist.org/help/support/policies/general-policies/use-of-online-resources-in-church-callings?lang=eng), cover the use of a stake website.
Those guidelines state:
When using images, videos, or personal information, consent from the content owner or the individuals involved is required. Consent may be obtained through a release form, a public announcement, a posted sign for a specific event, or written permission when needed. The country’s privacy laws should be followed.
The compilers for Stake/Ward histories are also supposed to get releases for the photographs they include.
A copy of the guidelines for histories is available here: https://www.churchofjesuschrist.org/callings/church-history-adviser/bc/pdf/stake-district-and-mission-annual-histories/2010-07-00-stake-district-and-mission-annual-histories-eng.pdf. Those guidelines also include a link to a release form (already linked above).