Add code samples for the "images and vision" page (#701)

* Add image generation code sample

* Add code samples for the "images and vision" page

* Update sample codes for images/vision

* Change the order of prompts to make all the samples consistent

Author: justinyoo

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

@@ -0,0 +1,39 @@
+// 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);
+
+Uri imageUrl = new("https://openai-documentation.vercel.app/images/cat_and_otter.png");
+using HttpClient http = new();
+
+// Download an image as stream
+using var stream = await http.GetStreamAsync(imageUrl);
+
+OpenAIResponse response1 = (OpenAIResponse)client.CreateResponse([
+    ResponseItem.CreateUserMessageItem([
+        ResponseContentPart.CreateInputTextPart("What is in this image?"),
+        ResponseContentPart.CreateInputImagePart(BinaryData.FromStream(stream), "image/png")
+    ])
+]);
+
+Console.WriteLine($"From image stream: {response1.GetOutputText()}");
+
+// Download an image as byte array
+byte[] bytes = await http.GetByteArrayAsync(imageUrl);
+
+OpenAIResponse response2 = (OpenAIResponse)client.CreateResponse([
+    ResponseItem.CreateUserMessageItem([
+        ResponseContentPart.CreateInputTextPart("What is in this image?"),
+        ResponseContentPart.CreateInputImagePart(BinaryData.FromBytes(bytes), "image/png")
+    ])
+]);
+
+Console.WriteLine($"From byte array: {response2.GetOutputText()}");

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

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+// 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);
+
+string filename = "cat_and_otter.png";
+Uri imageUrl = new($"https://openai-documentation.vercel.app/images/{filename}");
+using var http = new HttpClient();
+
+// Download an image as stream
+using var stream = await http.GetStreamAsync(imageUrl);
+
+OpenAIFileClient files = new(key);
+OpenAIFile file = await files.UploadFileAsync(BinaryData.FromStream(stream), filename, FileUploadPurpose.Vision);
+
+OpenAIResponse response = (OpenAIResponse)client.CreateResponse([
+    ResponseItem.CreateUserMessageItem([
+        ResponseContentPart.CreateInputTextPart("what's in this image?"),
+        ResponseContentPart.CreateInputImagePart(file.Id)
+    ])
+]);
+
+Console.WriteLine(response.GetOutputText());

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

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+// 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);
+
+Uri imageUrl = new("https://upload.wikimedia.org/wikipedia/commons/thumb/d/dd/Gfp-wisconsin-madison-the-nature-boardwalk.jpg/2560px-Gfp-wisconsin-madison-the-nature-boardwalk.jpg");
+
+OpenAIResponse response = (OpenAIResponse)client.CreateResponse([
+    ResponseItem.CreateUserMessageItem([
+        ResponseContentPart.CreateInputTextPart("What is in this image?"),
+        ResponseContentPart.CreateInputImagePart(imageUrl)
+    ])
+]);
+
+Console.WriteLine(response.GetOutputText());