Add code samples for the "images and vision" page

Author: justinyoo

docs/guides/images-vision/responses/analyze_images_passing_base64_string.cs

@@ -0,0 +1,50 @@
+// SAMPLE: Analyzes image by passing a base64-encoded image through Responses API
+// PAGE: https://platform.openai.com/docs/guides/images-vision?api-mode=responses&format=base64-encoded#analyze-images
+// GUIDANCE: Instructions to run this code: https://aka.ms/oai/net/start
+#pragma warning disable OPENAI001
+
+#:package OpenAI@2.*
+#:property PublishAot=false
+
+using OpenAI.Responses;
+
+string key = Environment.GetEnvironmentVariable("OPENAI_API_KEY")!;
+OpenAIResponseClient client = new(model: "gpt-5", apiKey: key);
+
+using var http = new HttpClient();
+
+// Download an image as stream
+using var stream = await http.GetStreamAsync("https://openai-documentation.vercel.app/images/cat_and_otter.png");
+
+OpenAIResponse response1 = (OpenAIResponse)client.CreateResponse([
+    ResponseItem.CreateUserMessageItem([
+        ResponseContentPart.CreateInputTextPart("What is in this image?"),
+        ResponseContentPart.CreateInputImagePart(BinaryData.FromStream(stream), "image/png")
+    ])
+]);
+
+Console.WriteLine($"From image stream: {response1.GetOutputText()}");
+
+// Download an image as byte array
+byte[] bytes = await http.GetByteArrayAsync("https://openai-documentation.vercel.app/images/cat_and_otter.png");
+
+OpenAIResponse response2 = (OpenAIResponse)client.CreateResponse([
+    ResponseItem.CreateUserMessageItem([
+        ResponseContentPart.CreateInputTextPart("What is in this image?"),
+        ResponseContentPart.CreateInputImagePart(BinaryData.FromBytes(bytes), "image/png")
+    ])
+]);
+
+Console.WriteLine($"From byte array: {response2.GetOutputText()}");
+
+// Convert the byte array to a base64 string
+string base64 = Convert.ToBase64String(bytes);
+
+OpenAIResponse response3 = (OpenAIResponse)client.CreateResponse([
+    ResponseItem.CreateUserMessageItem([
+        ResponseContentPart.CreateInputTextPart("What is in this image?"),
+        ResponseContentPart.CreateInputImagePart(BinaryData.FromString(base64), "image/png")
+    ])
+]);
+
+Console.WriteLine($"From base64 string: {response3.GetOutputText()}");

docs/guides/images-vision/responses/analyze_images_passing_file.cs

@@ -0,0 +1,30 @@
+// SAMPLE: Analyzes file from a file upload through Responses API
+// PAGE: https://platform.openai.com/docs/guides/images-vision?api-mode=responses&format=file#analyze-images
+// GUIDANCE: Instructions to run this code: https://aka.ms/oai/net/start
+#pragma warning disable OPENAI001
+
+#:package OpenAI@2.*
+#:property PublishAot=false
+
+using OpenAI.Files;
+using OpenAI.Responses;
+
+string key = Environment.GetEnvironmentVariable("OPENAI_API_KEY")!;
+OpenAIResponseClient client = new(model: "gpt-5", apiKey: key);
+
+using var http = new HttpClient();
+
+// Download an image as stream
+using var stream = await http.GetStreamAsync("https://openai-documentation.vercel.app/images/cat_and_otter.png");
+
+OpenAIFileClient files = new(key);
+OpenAIFile file = await files.UploadFileAsync(BinaryData.FromStream(stream), "cat_and_otter.png", FileUploadPurpose.Vision);
+
+OpenAIResponse response = (OpenAIResponse)client.CreateResponse([
+    ResponseItem.CreateUserMessageItem([
+        ResponseContentPart.CreateInputFilePart(file.Id),
+        ResponseContentPart.CreateInputTextPart("what's in this image?")
+    ])
+]);
+
+Console.WriteLine(response.GetOutputText());

docs/guides/images-vision/responses/analyze_images_passing_url.cs

@@ -0,0 +1,21 @@
+// SAMPLE: Analyzes image by passing an image URL through Responses API
+// PAGE: https://platform.openai.com/docs/guides/images-vision?api-mode=responses&format=url#analyze-images
+// GUIDANCE: Instructions to run this code: https://aka.ms/oai/net/start
+#pragma warning disable OPENAI001
+
+#:package OpenAI@2.*
+#:property PublishAot=false
+
+using OpenAI.Responses;
+
+string key = Environment.GetEnvironmentVariable("OPENAI_API_KEY")!;
+OpenAIResponseClient client = new(model: "gpt-5", apiKey: key);
+
+OpenAIResponse response = (OpenAIResponse)client.CreateResponse([
+    ResponseItem.CreateUserMessageItem([
+        ResponseContentPart.CreateInputTextPart("What is in this image?"),
+        ResponseContentPart.CreateInputImagePart(new Uri("https://upload.wikimedia.org/wikipedia/commons/thumb/d/dd/Gfp-wisconsin-madison-the-nature-boardwalk.jpg/2560px-Gfp-wisconsin-madison-the-nature-boardwalk.jpg"))
+    ])
+]);
+
+Console.WriteLine(response.GetOutputText());

docs/guides/images-vision/responses/generate-edit-images.cs

@@ -16,7 +16,7 @@
 OpenAIResponse response = (OpenAIResponse)client.CreateResponse(
         BinaryContent.Create(BinaryData.FromObjectAsJson(new
         {
-            model = "gpt-4.1",
+            model = "gpt-5",
             input = "Generate an image of gray tabby cat hugging an otter with an orange scarf",
             tools = new[]
             {