diff --git a/owocr/ocr.py b/owocr/ocr.py
index eda8fea..f2e2653 100644
--- a/owocr/ocr.py
+++ b/owocr/ocr.py
@@ -136,7 +136,7 @@ class GoogleVision:
 
     def _preprocess(self, img):
         image_bytes = io.BytesIO()
-        img.save(image_bytes, format=img.format)
+        img.save(image_bytes, format='png')
         return image_bytes.getvalue()
 
 class GoogleLens:
@@ -248,7 +248,7 @@ class AppleVision:
 
     def _preprocess(self, img):
         image_bytes = io.BytesIO()
-        img.save(image_bytes, format=img.format)
+        img.save(image_bytes, format='png')
         return image_bytes.getvalue()
 
 class WinRTOCR:
@@ -301,7 +301,7 @@ class WinRTOCR:
 
     def _preprocess(self, img):
         image_bytes = io.BytesIO()
-        img.save(image_bytes, format=img.format)
+        img.save(image_bytes, format='png')
         return image_bytes.getvalue()
 
 class AzureComputerVision:
@@ -353,7 +353,7 @@ class AzureComputerVision:
 
     def _preprocess(self, img):
         image_io = io.BytesIO()
-        img.save(image_io, format=img.format)
+        img.save(image_io, format='png')
         image_io.seek(0)
         return image_io
 
@@ -390,7 +390,7 @@ class EasyOCR:
 
     def _preprocess(self, img):
         image_bytes = io.BytesIO()
-        img.save(image_bytes, format=img.format)
+        img.save(image_bytes, format='png')
         return image_bytes.getvalue()
 
 class PaddleOCR:
diff --git a/owocr/run.py b/owocr/run.py
index 191f9fa..5904281 100644
--- a/owocr/run.py
+++ b/owocr/run.py
@@ -136,7 +136,7 @@ def user_input_thread_run(engine_instances, engine_keys, engine_color):
                 engine_index = 0
             else:
                 engine_index += 1
-        elif user_input.lower() in engine_keys:
+        elif user_input.lower() != '' and user_input.lower() in engine_keys:
             engine_index = engine_keys.index(user_input.lower())
 
         if engine_index != old_engine_index: