diff --git a/backend/src/main/java/com/edufocus/edufocus/lecture/controller/LectureController.java b/backend/src/main/java/com/edufocus/edufocus/lecture/controller/LectureController.java
index 7ad29a6..dfe142c 100644
--- a/backend/src/main/java/com/edufocus/edufocus/lecture/controller/LectureController.java
+++ b/backend/src/main/java/com/edufocus/edufocus/lecture/controller/LectureController.java
@@ -36,6 +36,10 @@ public class LectureController {
             return new ResponseEntity<>(HttpStatus.CONFLICT);
         }
 
+        if (!image.isEmpty() && !image.getContentType().startsWith("image")) {
+            return new ResponseEntity<>(HttpStatus.BAD_REQUEST);
+        }
+
         lectureService.createLecture(userId, lectureCreateRequest, image);
 
         return new ResponseEntity<>(HttpStatus.CREATED);
diff --git a/backend/src/main/java/com/edufocus/edufocus/quiz/controller/QuizController.java b/backend/src/main/java/com/edufocus/edufocus/quiz/controller/QuizController.java
index b1e3fe5..4a874c9 100644
--- a/backend/src/main/java/com/edufocus/edufocus/quiz/controller/QuizController.java
+++ b/backend/src/main/java/com/edufocus/edufocus/quiz/controller/QuizController.java
@@ -38,6 +38,12 @@ public class QuizController {
             return new ResponseEntity<>(HttpStatus.BAD_REQUEST);
         }
 
+        for (MultipartFile image : images) {
+            if (!image.isEmpty() && !image.getContentType().startsWith("image")) {
+                return new ResponseEntity<>(HttpStatus.BAD_REQUEST);
+            }
+        }
+
         QuizSet quizSet = quizSetService.createQuizSet(userId, quizSetCreateRequest.getTitle());
 
         int imageIdx = 0;
@@ -81,6 +87,12 @@ public class QuizController {
             return new ResponseEntity<>(HttpStatus.CONFLICT);
         }
 
+        for (MultipartFile image : images) {
+            if (!image.isEmpty() && !image.getContentType().startsWith("image")) {
+                return new ResponseEntity<>(HttpStatus.BAD_REQUEST);
+            }
+        }
+
         quizSetService.updateQuizSet(quizSetUpdateRequest.getId(), quizSetUpdateRequest.getTitle());
 
         Map<Long, Boolean> quizUpdatedCheckMap = new HashMap<>();