diff --git a/docs/content/doc/setup/install-frontend.md b/docs/content/doc/setup/install-frontend.md
index 77c2a610c..0a7130de6 100644
--- a/docs/content/doc/setup/install-frontend.md
+++ b/docs/content/doc/setup/install-frontend.md
@@ -47,10 +47,7 @@ which will run the docker image and expose port 80 on the host.
 
 See [full docker example]({{< ref "full-docker-example.md">}}) for more varations of this config.
 
-### Setting user and group id of the user running vikunja
-
-You can set the user and group id of the user running vikunja with the `PUID` and `PGID` evironment variables.
-This follows the pattern used by [the linuxserver.io](https://docs.linuxserver.io/general/understanding-puid-and-pgid) docker images.
+The docker container runs as an unprivileged user and does not mount anything.
 
 ### API URL configuration in docker
 
diff --git a/pkg/db/test.go b/pkg/db/test.go
index 7a5ff4f40..146643ffb 100644
--- a/pkg/db/test.go
+++ b/pkg/db/test.go
@@ -20,12 +20,12 @@ import (
 	"fmt"
 	"os"
 	"testing"
-	"xorm.io/builder"
 
 	"code.vikunja.io/api/pkg/config"
 	"code.vikunja.io/api/pkg/log"
 
 	"github.com/stretchr/testify/assert"
+	"xorm.io/builder"
 	"xorm.io/xorm"
 	"xorm.io/xorm/names"
 )
diff --git a/pkg/models/tasks_test.go b/pkg/models/tasks_test.go
index 96ac031bf..a6bbc71c4 100644
--- a/pkg/models/tasks_test.go
+++ b/pkg/models/tasks_test.go
@@ -19,13 +19,13 @@ package models
 import (
 	"testing"
 	"time"
-	"xorm.io/builder"
 
 	"code.vikunja.io/api/pkg/db"
 	"code.vikunja.io/api/pkg/events"
 	"code.vikunja.io/api/pkg/user"
 
 	"github.com/stretchr/testify/assert"
+	"xorm.io/builder"
 )
 
 func TestTask_Create(t *testing.T) {
diff --git a/pkg/modules/background/handler/background.go b/pkg/modules/background/handler/background.go
index dc57b23b5..6dfd74437 100644
--- a/pkg/modules/background/handler/background.go
+++ b/pkg/modules/background/handler/background.go
@@ -295,6 +295,11 @@ func GetListBackground(c echo.Context) error {
 		_ = s.Rollback()
 		return handler.HandleHTTPError(err, c)
 	}
+	stat, err := bgFile.File.Stat()
+	if err != nil {
+		_ = s.Rollback()
+		return handler.HandleHTTPError(err, c)
+	}
 
 	// Unsplash requires pingbacks as per their api usage guidelines.
 	// To do this in a privacy-preserving manner, we do the ping from inside of Vikunja to not expose any user details.
@@ -306,6 +311,11 @@ func GetListBackground(c echo.Context) error {
 		return handler.HandleHTTPError(err, c)
 	}
 
+	// Set Last-Modified header if we have the file stat, so clients can decide whether to use cached files
+	if stat != nil {
+		c.Response().Header().Set(echo.HeaderLastModified, stat.ModTime().UTC().Format(http.TimeFormat))
+	}
+
 	// Serve the file
 	return c.Stream(http.StatusOK, "image/jpg", bgFile.File)
 }