diff --git a/openAIImages.m b/openAIImages.m
index e60aa16..479c60a 100644
--- a/openAIImages.m
+++ b/openAIImages.m
@@ -85,8 +85,8 @@
             %                          Only "dall-e-3" supports this parameter.
 
             arguments
-                this                    (1,1)  openAIImages
-                prompt                        {mustBeTextScalar}
+                this                    (1,1) openAIImages
+                prompt                        {mustBeNonzeroLengthTextScalar}
                 nvp.NumImages           (1,1) {mustBePositive, mustBeInteger,...
                                                 mustBeLessThanOrEqual(nvp.NumImages,10)} = 1
                 nvp.Size                (1,1) string {mustBeMember(nvp.Size, ["256x256", "512x512", ...
@@ -176,7 +176,7 @@
             arguments
                 this                    (1,1)  openAIImages
                 imagePath                     {mustBeValidFileType(imagePath)}
-                prompt                        {mustBeTextScalar}
+                prompt                        {mustBeNonzeroLengthTextScalar}
                 nvp.MaskImagePath             {mustBeValidFileType(nvp.MaskImagePath)}
                 nvp.NumImages           (1,1) {mustBePositive, mustBeInteger,...
                                                 mustBeLessThanOrEqual(nvp.NumImages,10)} = 1
@@ -345,7 +345,9 @@ function validatePromptSize(model, prompt)
 function mustBeValidFileType(filePath)
     mustBeFile(filePath);
     s = dir(filePath);
-    if ~endsWith(s.name, ".png")
+    imgDetails = imfinfo(filePath);
+    imgFormat = imgDetails.Format;
+    if ~(imgFormat=="png")
         error("llms:pngExpected", ...
             llms.utils.errorMessageCatalog.getMessage("llms:pngExpected"));
     end
diff --git a/tests/test_files/solar.png b/tests/test_files/solar.png
new file mode 100644
index 0000000..fc37277
Binary files /dev/null and b/tests/test_files/solar.png differ
diff --git a/tests/topenAIImages.m b/tests/topenAIImages.m
index 4e70f9a..2b625e1 100644
--- a/tests/topenAIImages.m
+++ b/tests/topenAIImages.m
@@ -105,6 +105,12 @@ function constructModelWithAllNVP(testCase)
             testCase.verifyEqual(mdl.ModelName, modelName);
         end
 
+        function fakePNGImage(testCase)
+            mdl = openAIImages(ApiKey="this-is-not-a-real-key");
+            fakePng = fullfile("test_files", "solar.png");
+            testCase.verifyError(@()edit(mdl,fakePng, "bla"), "llms:pngExpected");
+        end
+
         function invalidInputsConstructor(testCase, InvalidConstructorInput)
             testCase.verifyError(@()openAIImages(InvalidConstructorInput.Input{:}), InvalidConstructorInput.Error);
         end
@@ -157,11 +163,15 @@ function invalidInputsVariation(testCase, InvalidVariationInput)
 invalidGenerateInput = struct( ...
         "EmptyInput",struct( ...
             "Input",{{ [] }},...
-            "Error","MATLAB:validators:mustBeTextScalar"),...
+            "Error","MATLAB:validators:mustBeNonzeroLengthText"),...
         ...
         "InvalidInputType",struct( ...
             "Input",{{ 123 }},...
-            "Error","MATLAB:validators:mustBeTextScalar"),...
+            "Error","MATLAB:validators:mustBeNonzeroLengthText"),...
+        ...
+         "InvalidPromptLen",struct( ...
+            "Input",{{ "" }},...
+            "Error","MATLAB:validators:mustBeNonzeroLengthText"),...
         ...
         "InvalidNumImagesType",struct( ...
             "Input",{{ "prompt"  "NumImages" "2" }},...
@@ -233,17 +243,21 @@ function invalidInputsVariation(testCase, InvalidVariationInput)
             "Input",{{ 123, "prompt" }},...
             "Error","MATLAB:validators:mustBeNonzeroLengthText"),...
         ...
+        "InvalidPromptLen",struct( ...
+            "Input",{{ validImage, "" }},...
+            "Error","MATLAB:validators:mustBeNonzeroLengthText"),...
+        ...
         "InvalidImageExtension",struct( ...
             "Input",{{ nonPNGImage, "prompt" }},...
             "Error","llms:pngExpected"),...
         ...
         "EmptyPrompt",struct( ...
             "Input",{{ validImage, [] }},...
-            "Error","MATLAB:validators:mustBeTextScalar"),...
+            "Error","MATLAB:validators:mustBeNonzeroLengthText"),...
         ...
         "InvalidPromptType",struct( ...
             "Input",{{ validImage, 123 }},...
-            "Error","MATLAB:validators:mustBeTextScalar"),...
+            "Error","MATLAB:validators:mustBeNonzeroLengthText"),...
         ...
         "InvalidMaskImage",struct( ...
             "Input",{{ validImage, "foo", "MaskImagePath", 123 }},...