diff --git a/internal/openai/chat_prepare.go b/internal/openai/chat_prepare.go
index 50afaa8..4e4478e 100644
--- a/internal/openai/chat_prepare.go
+++ b/internal/openai/chat_prepare.go
@@ -467,6 +467,16 @@ func (p *chatPreparer) prepareMessageContent(raw any, path string, allowImages b
 			}
 			out = append(out, map[string]any{"type": "image_url", "image_url": image})
 			p.recordUnknownObjectFields(part, map[string]bool{"type": true, "image_url": true}, partPath)
+		case "image":
+			if !allowImages {
+				return nil, fmt.Errorf("%s.type image is only valid for user messages", partPath)
+			}
+			image, err := p.prepareAnthropicImage(part, partPath)
+			if err != nil {
+				return nil, err
+			}
+			out = append(out, map[string]any{"type": "image_url", "image_url": image})
+			p.recordUnknownObjectFields(part, map[string]bool{"type": true, "source": true}, partPath)
 		default:
 			return nil, fmt.Errorf("%s.type %q is not supported", partPath, kind)
 		}
@@ -474,6 +484,34 @@ func (p *chatPreparer) prepareMessageContent(raw any, path string, allowImages b
 	return out, nil
 }
 
+func (p *chatPreparer) prepareAnthropicImage(block map[string]any, path string) (map[string]any, error) {
+	source, ok := block["source"].(map[string]any)
+	if !ok {
+		return nil, fmt.Errorf("%s.source must be an object", path)
+	}
+	var url string
+	switch sourceType, _ := source["type"].(string); sourceType {
+	case "url":
+		value, ok := source["url"].(string)
+		if !ok || strings.TrimSpace(value) == "" {
+			return nil, fmt.Errorf("%s.source.url must be a non-empty string", path)
+		}
+		url = value
+	case "base64":
+		mediaType, _ := source["media_type"].(string)
+		data, _ := source["data"].(string)
+		if strings.TrimSpace(mediaType) == "" || strings.TrimSpace(data) == "" {
+			return nil, fmt.Errorf("%s.source media_type and data are required for base64 images", path)
+		}
+		url = "data:" + mediaType + ";base64," + data
+	default:
+		return nil, fmt.Errorf("%s.source.type %q is not supported", path, sourceType)
+	}
+	p.recordUnknownObjectFields(source, map[string]bool{"type": true, "url": true, "media_type": true, "data": true}, path+".source")
+	p.change(path, "rewritten", "Anthropic image block is normalized to OpenAI image_url content")
+	return map[string]any{"url": url}, nil
+}
+
 func (p *chatPreparer) prepareImageURL(raw any, path string) (map[string]any, error) {
 	if value, ok := raw.(string); ok && strings.TrimSpace(value) != "" {
 		p.change(path, "rewritten", "string image URL is normalized to an object")
diff --git a/internal/openai/chat_prepare_test.go b/internal/openai/chat_prepare_test.go
index d2501b4..2b60d3e 100644
--- a/internal/openai/chat_prepare_test.go
+++ b/internal/openai/chat_prepare_test.go
@@ -66,6 +66,7 @@ func TestPrepareChatNormalizesMessagesAndToolHistory(t *testing.T) {
 			map[string]any{"role": "user", "content": []any{
 				map[string]any{"type": "text", "text": "inspect", "cache_control": true},
 				map[string]any{"type": "image_url", "image_url": map[string]any{"url": "data:image/png;base64,AA", "detail": "low", "vendor": true}},
+				map[string]any{"type": "image", "source": map[string]any{"type": "base64", "media_type": "image/png", "data": "BB", "vendor": true}, "cache_control": true},
 			}},
 			map[string]any{"role": "assistant", "content": nil, "reasoning_content": "need tool", "tool_calls": []any{
 				map[string]any{"id": "call-1", "type": "function", "function": map[string]any{"name": "lookup", "arguments": `{"id":1}`, "extra": true}},
@@ -82,11 +83,15 @@ func TestPrepareChatNormalizesMessagesAndToolHistory(t *testing.T) {
 	if parts[0].(map[string]any)["cache_control"] != nil || parts[1].(map[string]any)["image_url"].(map[string]any)["vendor"] != nil {
 		t.Fatalf("content metadata leaked: %#v", parts)
 	}
+	convertedImage := parts[2].(map[string]any)
+	if convertedImage["type"] != "image_url" || convertedImage["image_url"].(map[string]any)["url"] != "data:image/png;base64,BB" {
+		t.Fatalf("Anthropic image block was not normalized: %#v", convertedImage)
+	}
 	call := messages[2].(map[string]any)["tool_calls"].([]any)[0].(map[string]any)
 	if call["function"].(map[string]any)["extra"] != nil {
 		t.Fatalf("tool call metadata leaked: %#v", call)
 	}
-	for _, path := range []string{"messages[0].role", "messages[0].cache_control", "messages[1].content[0].cache_control", "messages[2].tool_calls[0].function.extra"} {
+	for _, path := range []string{"messages[0].role", "messages[0].cache_control", "messages[1].content[0].cache_control", "messages[1].content[2]", "messages[2].tool_calls[0].function.extra"} {
 		if !hasChatChange(prepared.Changes, path) {
 			t.Fatalf("missing change for %s", path)
 		}