diff --git a/README.md b/README.md
index cb51fe34..b8864eb6 100644
--- a/README.md
+++ b/README.md
@@ -853,6 +853,9 @@ Valid filters are:
  • braces: Enclose value in curly braces, e.g. 'value => '{value}'.             
  • parens: Enclose value in parentheses, e.g. 'value' => '(value')              
  • brackets: Enclose value in brackets, e.g. 'value' => '[value]'               
+ • function: Run custom python function to filter value; use in format          
+   'function:/path/to/file.py::function_name'. See example at https://github.com
+   /RhetTbull/osxphotos/blob/master/examples/template_filter.py                 
 
 e.g. if Photo keywords are ["FOO","bar"]:                                       
 
@@ -2226,6 +2229,7 @@ Valid filters are:
 - braces: Enclose value in curly braces, e.g. 'value => '{value}'.
 - parens: Enclose value in parentheses, e.g. 'value' => '(value')
 - brackets: Enclose value in brackets, e.g. 'value' => '[value]'
+- function: Run custom python function to filter value; use in format 'function:/path/to/file.py::function_name'. See example at https://github.com/RhetTbull/osxphotos/blob/master/examples/template_filter.py
 <!-- OSXPHOTOS-FILTER-TABLE:END -->
 
 e.g. if Photo keywords are `["FOO","bar"]`:
diff --git a/osxphotos/_version.py b/osxphotos/_version.py
index e41e6710..2478b78d 100644
--- a/osxphotos/_version.py
+++ b/osxphotos/_version.py
@@ -1,3 +1,3 @@
 """ version info """
 
-__version__ = "0.42.7"
+__version__ = "0.42.8"
diff --git a/osxphotos/phototemplate.md b/osxphotos/phototemplate.md
index fc6033fd..603a43dd 100644
--- a/osxphotos/phototemplate.md
+++ b/osxphotos/phototemplate.md
@@ -39,6 +39,7 @@ Valid filters are:
 - braces: Enclose value in curly braces, e.g. 'value => '{value}'.
 - parens: Enclose value in parentheses, e.g. 'value' => '(value')
 - brackets: Enclose value in brackets, e.g. 'value' => '[value]'
+- function: Run custom python function to filter value; use in format 'function:/path/to/file.py::function_name'. See example at https://github.com/RhetTbull/osxphotos/blob/master/examples/template_filter.py
 <!-- OSXPHOTOS-FILTER-TABLE:END -->
 
 e.g. if Photo keywords are `["FOO","bar"]`:
diff --git a/osxphotos/phototemplate.py b/osxphotos/phototemplate.py
index b0168939..6af83093 100644
--- a/osxphotos/phototemplate.py
+++ b/osxphotos/phototemplate.py
@@ -174,6 +174,7 @@ FILTER_VALUES = {
     "braces": "Enclose value in curly braces, e.g. 'value => '{value}'.",
     "parens": "Enclose value in parentheses, e.g. 'value' => '(value')",
     "brackets": "Enclose value in brackets, e.g. 'value' => '[value]'",
+    "function": "Run custom python function to filter value; use in format 'function:/path/to/file.py::function_name'. See example at https://github.com/RhetTbull/osxphotos/blob/master/examples/template_filter.py"
 }
 
 # Just the substitutions without the braces