diff --git a/internal/images/images.go b/internal/images/images.go
index b447c27f2..5f7ed21f2 100644
--- a/internal/images/images.go
+++ b/internal/images/images.go
@@ -57,7 +57,7 @@ var ErrHEIC = errors.New("HEIC decoding not implemented yet")
 
 func init() {
 	image.RegisterFormat("heic",
-		"????ftypheic????????????????meta????????hdlr????????pict",
+		"????ftypheic",
 		func(io.Reader) (image.Image, error) {
 			return nil, ErrHEIC
 		},
@@ -364,7 +364,7 @@ var debug, _ = strconv.ParseBool(os.Getenv("CAMLI_DEBUG_IMAGES"))
 
 func imageDebug(msg string) {
 	if debug {
-		log.Print(msg)
+		log.Print("internal/images: " + msg)
 	}
 }
 
@@ -396,7 +396,9 @@ func DecodeConfig(r io.Reader) (Config, error) {
 
 	conf, format, err := image.DecodeConfig(tr)
 	if err != nil {
-		imageDebug(fmt.Sprintf("Image Decoding failed: %v", err))
+		if debug {
+			log.Printf("internal/images: DecodeConfig failed after reading %d bytes: %v", buf.Len(), err)
+		}
 		return Config{}, err
 	}
 	c := Config{
diff --git a/internal/images/images_test.go b/internal/images/images_test.go
index 0f908c8eb..d8a3aef02 100644
--- a/internal/images/images_test.go
+++ b/internal/images/images_test.go
@@ -18,6 +18,7 @@ package images
 
 import (
 	"bytes"
+	"fmt"
 	"image"
 	"image/jpeg"
 	"io"
@@ -377,7 +378,7 @@ func TestIssue513(t *testing.T) {
 	}
 }
 
-func TestHEIF(t *testing.T) {
+func TestHEIFToJPEG(t *testing.T) {
 	filename := filepath.Join("testdata", "IMG_8062.HEIC")
 	f, err := os.Open(filename)
 	if err != nil {
@@ -402,3 +403,22 @@ func TestHEIF(t *testing.T) {
 		t.Fatalf("wrong width or height, wanted (%d, %d), got (%d, %d)", wantWidth, wantHeight, conf.Width, conf.Height)
 	}
 }
+
+func TestDecodeHEIC_WithJPEGInHeader(t *testing.T) {
+	filename := filepath.Join("testdata", "river-truncated.heic")
+	f, err := os.Open(filename)
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer f.Close()
+
+	conf, err := DecodeConfig(f)
+	if err != nil {
+		t.Fatal(err)
+	}
+	got := fmt.Sprintf("Width:%d Height:%d Format:%v HEIC:%d bytes", conf.Width, conf.Height, conf.Format, len(conf.HEICEXIF))
+	want := "Width:6302 Height:3912 Format:heic HEIC:1046 bytes"
+	if got != want {
+		t.Errorf("Got:\n  %s\nWant:\n  %s", got, want)
+	}
+}
diff --git a/internal/images/testdata/river-truncated.heic b/internal/images/testdata/river-truncated.heic
new file mode 100644
index 000000000..407be0d6d
Binary files /dev/null and b/internal/images/testdata/river-truncated.heic differ
diff --git a/pkg/index/receive.go b/pkg/index/receive.go
index f22606073..b592f0f51 100644
--- a/pkg/index/receive.go
+++ b/pkg/index/receive.go
@@ -248,6 +248,9 @@ func (ix *Index) ReceiveBlob(ctx context.Context, blobRef blob.Ref, source io.Re
 	}
 
 	mm, err := ix.populateMutationMap(ctx, fetcher, blobRef, sniffer)
+	if debugEnv {
+		log.Printf("index of %v: mm=%v, err=%v", blobRef, mm, err)
+	}
 	if err != nil {
 		if err != errMissingDep {
 			return blob.SizedRef{}, err
@@ -503,6 +506,8 @@ func (ix *Index) populateFile(ctx context.Context, fetcher blob.Fetcher, b *sche
 		}
 		if err := readPrefixOrFile(imageBuf.Bytes, fetcher, b, decodeConfig); err == nil {
 			mm.Set(keyImageSize.Key(blobRef), keyImageSize.Val(fmt.Sprint(conf.Width), fmt.Sprint(conf.Height)))
+		} else if debugEnv {
+			log.Printf("index: WARNING: image decodeConfig: %v", err)
 		}
 
 		exifData := imageBuf.Bytes
@@ -517,6 +522,9 @@ func (ix *Index) populateFile(ctx context.Context, fetcher blob.Fetcher, b *sche
 
 		if err = readPrefixOrFile(exifData, fetcher, b, fileTime); err == nil {
 			times = append(times, ft)
+		} else if debugEnv {
+			log.Printf("index: WARNING: image fileTime: %v", err)
+
 		}
 		if exifDebug {
 			log.Printf("filename %q exif = %v, %v", b.FileName(), ft, err)