diff --git a/imptune/config.py b/imptune/config.py
index bb55eeb..125792a 100644
--- a/imptune/config.py
+++ b/imptune/config.py
@@ -10,3 +10,4 @@ PORT = int(os.environ.get("PORT", "8000"))
 
 DB_PATH = str(Path(DATA_DIR) / "imptune.db")
 DRIVERS_DIR = str(Path(DATA_DIR) / "drivers")
+ICONS_DIR = str(Path(DATA_DIR) / "icons")
diff --git a/requirements.txt b/requirements.txt
index a3ed5b2..c3a08eb 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -5,3 +5,4 @@ python-multipart==0.0.9
 pycryptodome==3.20.*
 python-dotenv==1.0.*
 peewee==3.17.*
+Pillow>=10.0
diff --git a/tests/test_icon_upload.py b/tests/test_icon_upload.py
new file mode 100644
index 0000000..f87b237
--- /dev/null
+++ b/tests/test_icon_upload.py
@@ -0,0 +1,140 @@
+"""Integration tests for icon upload endpoint — PKG-04."""
+from __future__ import annotations
+
+import io
+
+import pytest
+from PIL import Image
+
+
+def _make_png(width: int = 256, height: int = 256, size_bytes: int | None = None) -> bytes:
+    """Create a valid PNG image with given dimensions in memory."""
+    img = Image.new("RGBA", (width, height), color="red")
+    buf = io.BytesIO()
+    img.save(buf, format="PNG")
+    data = buf.getvalue()
+    if size_bytes is not None and size_bytes > len(data):
+        # Pad the PNG by embedding extra data (won't affect PIL open, but will exceed size limit)
+        # Instead, use a raw bytes approach: return oversized raw content
+        data = data + b"\x00" * (size_bytes - len(data))
+    return data
+
+
+def _make_jpeg(width: int = 256, height: int = 256) -> bytes:
+    """Create a valid JPEG image with given dimensions in memory."""
+    img = Image.new("RGB", (width, height), color="blue")
+    buf = io.BytesIO()
+    img.save(buf, format="JPEG")
+    return buf.getvalue()
+
+
+def _create_printer(client):
+    """Create a test Printer record and return it."""
+    from imptune.db.models import Printer
+
+    return Printer.create(
+        name="Test Printer",
+        ip_address="10.0.0.1",
+        port_name="IP_10.0.0.1",
+    )
+
+
+class TestIconUpload:
+    def test_upload_valid_png(self, client, tmp_data_dir):
+        """POST a valid 256x256 PNG returns 200 and Icon record created."""
+        from imptune.db.models import Icon
+
+        printer = _create_printer(client)
+        png_data = _make_png(256, 256)
+        response = client.post(
+            f"/printers/{printer.id}/icon",
+            files={"file": ("icon.png", io.BytesIO(png_data), "image/png")},
+        )
+        assert response.status_code == 200
+        assert "Icon uploaded successfully" in response.text
+
+        icons = list(Icon.select().where(Icon.printer == printer.id))
+        assert len(icons) == 1
+        assert icons[0].original_filename == "icon.png"
+
+        # File must be stored on disk
+        import hashlib
+        from pathlib import Path
+
+        sha256 = hashlib.sha256(png_data).hexdigest()
+        icon_file = Path(tmp_data_dir) / "icons" / sha256
+        assert icon_file.exists()
+
+    def test_reject_non_png(self, client, tmp_data_dir):
+        """POST with a JPEG file returns 422 with PNG format error."""
+        printer = _create_printer(client)
+        jpeg_data = _make_jpeg(256, 256)
+        response = client.post(
+            f"/printers/{printer.id}/icon",
+            files={"file": ("icon.jpg", io.BytesIO(jpeg_data), "image/jpeg")},
+        )
+        assert response.status_code == 422
+        assert "PNG" in response.text
+
+    def test_reject_oversized(self, client, tmp_data_dir):
+        """POST with PNG > 750KB returns 422 with 750 KB error."""
+        printer = _create_printer(client)
+        # Craft oversized data: valid PNG bytes followed by padding
+        png_bytes = _make_png(256, 256)
+        oversized = png_bytes + b"\x00" * (750 * 1024 + 1 - len(png_bytes))
+        response = client.post(
+            f"/printers/{printer.id}/icon",
+            files={"file": ("big.png", io.BytesIO(oversized), "image/png")},
+        )
+        assert response.status_code == 422
+        assert "750" in response.text
+
+    def test_reject_wrong_dimensions(self, client, tmp_data_dir):
+        """POST with 128x128 PNG returns 422 with 256x256 error."""
+        printer = _create_printer(client)
+        png_data = _make_png(128, 128)
+        response = client.post(
+            f"/printers/{printer.id}/icon",
+            files={"file": ("small.png", io.BytesIO(png_data), "image/png")},
+        )
+        assert response.status_code == 422
+        assert "256x256" in response.text
+
+    def test_replace_existing_icon(self, client, tmp_data_dir):
+        """Second upload for same printer replaces the Icon record."""
+        from imptune.db.models import Icon
+
+        printer = _create_printer(client)
+
+        # First upload
+        png1 = _make_png(256, 256)
+        client.post(
+            f"/printers/{printer.id}/icon",
+            files={"file": ("icon1.png", io.BytesIO(png1), "image/png")},
+        )
+
+        # Second upload (different color to get different sha256)
+        img2 = Image.new("RGBA", (256, 256), color="green")
+        buf2 = io.BytesIO()
+        img2.save(buf2, format="PNG")
+        png2 = buf2.getvalue()
+
+        response = client.post(
+            f"/printers/{printer.id}/icon",
+            files={"file": ("icon2.png", io.BytesIO(png2), "image/png")},
+        )
+        assert response.status_code == 200
+
+        # Still only one Icon record for this printer
+        icons = list(Icon.select().where(Icon.printer == printer.id))
+        assert len(icons) == 1
+        assert icons[0].original_filename == "icon2.png"
+
+    def test_404_missing_printer(self, client, tmp_data_dir):
+        """POST to nonexistent printer_id returns 404."""
+        png_data = _make_png(256, 256)
+        response = client.post(
+            "/printers/99999/icon",
+            files={"file": ("icon.png", io.BytesIO(png_data), "image/png")},
+        )
+        assert response.status_code == 404