diff --git a/ledsa/core/ConfigData.py b/ledsa/core/ConfigData.py
index 75a3f7a..951a4f0 100644
--- a/ledsa/core/ConfigData.py
+++ b/ledsa/core/ConfigData.py
@@ -314,7 +314,8 @@ def in_time_diff_to_img_time(self) -> None:
         if has_id:
             generated_path = os.path.abspath(os.path.join(
                 self['DEFAULT']['img_directory'],
-                self['DEFAULT']['img_name_string'].format(self['DEFAULT']['time_ref_img_id'])
+                # the ID is read as a string, a format spec like {:04d} needs it as a number
+                self['DEFAULT']['img_name_string'].format(int(self['DEFAULT']['time_ref_img_id']))
             ))
 
         if has_file:
@@ -422,7 +423,7 @@ def get_start_time(self) -> None:
         """
         time_img = get_exif_datetime(os.path.join(self['DEFAULT']['img_directory'],
                                                   self['DEFAULT']['img_name_string'].format(
-                                                      self['DEFAULT']['first_img_experiment_id'])),
+                                                      int(self['DEFAULT']['first_img_experiment_id']))),
                                      'DateTimeOriginal')
         start_time = time_img - timedelta(seconds=self['DEFAULT'].getfloat('exif_time_infront_real_time'))
         time_format = '%H:%M:%S' if start_time.microsecond == 0 else '%H:%M:%S.%f'
diff --git a/ledsa/tests/AcceptanceTests/09_test_image_names.robot b/ledsa/tests/AcceptanceTests/09_test_image_names.robot
new file mode 100644
index 0000000..d49f292
--- /dev/null
+++ b/ledsa/tests/AcceptanceTests/09_test_image_names.robot
@@ -0,0 +1,48 @@
+*** Settings ***
+Resource  global_keywords.resource
+
+Force Tags  image_names
+
+*** Test Cases ***
+Zero Padded Image IDs With A Format Spec
+    [Documentation]    Most cameras write zero padded image IDs (DSC_0001.CR3), for which the config
+    ...                documents a format spec such as {:04d}. The whole workflow must accept it, including
+    ...                the start time, which is read from the first image when it is not set.
+    Prepare Padded Image IDs    padded_ids
+    Run Workflow And Check Results
+
+Time Reference Image With A Zero Padded ID
+    [Documentation]    The camera clock offset can be computed from a time reference image given by its ID,
+    ...                which is formatted with the same template. The first test image shows 12:00:00.
+    Prepare Padded Image IDs    padded_time_reference
+    Set Config Option    DEFAULT    exif_time_infront_real_time    None
+    Set Config Option    DEFAULT    time_ref_img_id    1
+    Set Config Option    DEFAULT    time_ref_img_time    12:00:00
+    Run Workflow And Check Results
+
+*** Keywords ***
+Prepare Padded Image IDs
+    [Arguments]    ${dir}
+    Create Directory    ${WORKDIR}${/}${dir}
+    Change Directory    ${WORKDIR}${/}${dir}
+    Create Test Data
+    Rename Test Images To Padded IDs
+    Create Config
+    Set Config Option    DEFAULT    img_name_string    test_img_{:04d}.jpg
+
+Run Workflow And Check Results
+    Execute Ledsa    -s1
+    Execute Ledsa    -s2
+    Execute Ledsa    --coordinates
+    Execute Ledsa    -s3_fast
+    Analysed Image Names Should Be    test_img_0001.jpg    test_img_0002.jpg    test_img_0003.jpg    test_img_0004.jpg
+    Create And Fill Config Analysis    linear
+    Execute Ledsa    --analysis
+    Check Padded Results    2
+    Check Padded Results    3
+    Check Padded Results    4
+
+Check Padded Results
+    [Arguments]    ${image_id}
+    ${rmse} =    Check Input Vs Computed Extinction Coefficients    ${image_id}    linear
+    Should Be True    ${rmse} < 0.05
diff --git a/ledsa/tests/AcceptanceTests/LedsaATestLibrary.py b/ledsa/tests/AcceptanceTests/LedsaATestLibrary.py
index 9146831..987c803 100644
--- a/ledsa/tests/AcceptanceTests/LedsaATestLibrary.py
+++ b/ledsa/tests/AcceptanceTests/LedsaATestLibrary.py
@@ -480,6 +480,20 @@ def get_analysis_image_id(self, img_name):
                     return img_id
         raise AssertionError(f'{img_name} is not listed in {file_path}')
 
+    @keyword
+    def rename_test_images_to_padded_ids(self, num_digits=4):
+        """Rename test_data/test_img_<id>.jpg to zero padded IDs (test_img_0001.jpg), as most cameras write them."""
+        for path in glob.glob(os.path.join('test_data', 'test_img_*.jpg')):
+            img_id = int(os.path.basename(path)[len('test_img_'):-len('.jpg')])
+            os.rename(path, os.path.join('test_data', f'test_img_{img_id:0{int(num_digits)}d}.jpg'))
+
+    @keyword
+    def set_config_option(self, section, option, value):
+        """Set an option in the config.ini of the current directory."""
+        conf = ConfigData()
+        conf[section][option] = str(value)
+        conf.save()
+
     @keyword
     def analysed_image_names_should_be(self, *expected_img_names):
         """Fail unless exactly the given images are listed in 'image_infos_analysis.csv'."""