Fix versions with leading v, e.g. v5.0

src/ocrmypdf/exec/__init__.py

@@ -271,6 +271,14 @@ def check_external_program(
             raise MissingDependencyError()
         return
 
+    def remove_leading_v(s):
+        if s.startswith('v'):
+            return s[1:]
+        return s
+
+    found_version = remove_leading_v(found_version)
+    need_version = remove_leading_v(need_version)
+
     if LooseVersion(found_version) < LooseVersion(need_version):
         _error_old_version(program, package, need_version, found_version, required_for)
         if not recommended:

tests/test_validation.py

@@ -197,6 +197,12 @@ def test_version_comparison():
         version_checker=lambda: '4.0.0-beta.1',
         need_version='4.0.0',
     )
+    vd.check_external_program(
+        program="tesseract",
+        package="tesseract",
+        version_checker=lambda: 'v5.0.0-alpha.20200201',
+        need_version='4.0.0',
+    )
     with pytest.raises(MissingDependencyError):
         vd.check_external_program(
             program="dummy_fails",