n_frames is incorrect for JPG image

<!-- Thank you for reporting an issue. Follow these guidelines to ensure your issue is handled properly. If you have a ... 1. General question: consider asking the question on Stack Overflow with the python-imaging-library tag: * https://stackoverflow.com/questions/tagged/python-imaging-library Do not ask a question in both places. If you think you have found a bug or have an unexplained exception then file a bug report here. 2. Bug report: include a self-contained, copy-pastable example that generates the issue if possible. Be concise with code posted. Guidelines on how to provide a good bug report: * https://stackoverflow.com/help/mcve Bug reports which follow these guidelines are easier to diagnose, and are often handled much more quickly. 3. Feature request: do a quick search of existing issues to make sure this has not been asked before. We know asking good questions takes effort, and we appreciate your time. Thank you. --> ### What did you do? Loading the attached JPG image via `img = PIL.Image.open(...)` ### What did you expect to happen? `img.n_frames == 1` ### What actually happened? `img.n_frames == 2` However, `img.seek(1)` raises an exception. This becomes problematic in downstream tasks like easy.thumbnails' scale-and-crop plugin which applies the command to all frames but fails for the second frame. A similar problem is reported here: https://github.com/SmileyChris/easy-thumbnails/issues/660 I am not sure why or if this JPG has 2 frames. GIMP reports only a single layer. This may be entirely a problem of the image itself. However, i find it strange that the 2nd frame is reported although it seems to have no data. ### What are your OS, Python and Pillow versions? * OS: debian/ubuntu (official python docker image) * Python: 2.7 & 3.13 * Pillow: 6.2.2 & 12.2 (I just included an older version of Pillow to make sure it's not a recent problem) ```text -------------------------------------------------------------------- Pillow 6.2.2 -------------------------------------------------------------------- Python modules loaded from /usr/local/lib/python2.7/site-packages/PIL Binary modules loaded from /usr/local/lib/python2.7/site-packages/PIL -------------------------------------------------------------------- Python 2.7.18 (default, Apr 20 2020, 19:27:10) [GCC 8.3.0] -------------------------------------------------------------------- --- PIL CORE support ok --- TKINTER support ok --- FREETYPE2 support ok --- LITTLECMS2 support ok --- WEBP support ok --- WEBP Transparency support ok --- WEBPMUX support ok --- WEBP Animation support ok --- JPEG support ok --- OPENJPEG (JPEG2000) support ok --- ZLIB (PNG/ZIP) support ok --- LIBTIFF support ok *** RAQM (Bidirectional Text) support not installed -------------------------------------------------------------------- ``` ```text -------------------------------------------------------------------- Pillow 12.2.0 Python 3.14.5 (main, May 11 2026, 23:12:59) [GCC 14.2.0] -------------------------------------------------------------------- Python executable is /usr/local/bin/python System Python files loaded from /usr/local -------------------------------------------------------------------- Python Pillow modules loaded from /usr/local/lib/python3.14/site-packages/PIL Binary Pillow modules loaded from /usr/local/lib/python3.14/site-packages/PIL -------------------------------------------------------------------- --- PIL CORE support ok, compiled for 12.2.0 --- TKINTER support ok, loaded 8.6 --- FREETYPE2 support ok, loaded 2.14.3 --- LITTLECMS2 support ok, loaded 2.18 --- WEBP support ok, loaded 1.6.0 --- AVIF support ok, loaded 1.4.1 --- JPEG support ok, compiled for libjpeg-turbo 3.1.4.1 --- OPENJPEG (JPEG2000) support ok, loaded 2.5.4 --- ZLIB (PNG/ZIP) support ok, loaded 1.3.1, compiled for zlib-ng 2.3.3 --- LIBTIFF support ok, loaded 4.7.1 --- RAQM (Bidirectional Text) support ok, loaded 0.10.3, fribidi 1.0.16, harfbuzz 13.2.1 *** LIBIMAGEQUANT (Quantization method) support not installed --- XCB (X protocol) support ok -------------------------------------------------------------------- ``` <!-- Please include **code** that reproduces the issue and whenever possible, an **image** that demonstrates the issue. Please upload images to GitHub, not to third-party file hosting sites. If necessary, add the image to a zip or tar archive. The best reproductions are self-contained scripts with minimal dependencies. If you are using a framework such as Plone, Django, or Buildout, try to replicate the issue just using Pillow. --> #### Dockerimage ``` FROM python:3 WORKDIR /usr/src/app RUN pip install --no-cache-dir Pillow COPY . . CMD [ "python", "./test.py" ] ``` #### test.py ```python import PIL.Image img = PIL.Image.open("Borago_officinalis_2015-11-18.JPG") print("n_frames={}".format(img.n_frames)) for i in range(img.n_frames): try: img.seek(i) print("seek({}): OK".format(i)) except Exception as e: print("seek({}): {}: {}".format(i, type(e).__name__, e)) ``` #### output of Pillow 6.2 ``` n_frames=2 seek(0): OK seek(1): error: unpack_from requires a buffer of at least 2 bytes ``` #### output of Pillow 12.2 ``` n_frames=2 seek(0): OK seek(1): ValueError: No data found for frame ``` <img width="4000" height="3000" alt="Image" src="https://github.com/user-attachments/assets/8d77cc43-1b7a-407a-941c-d7270b45ae1d" /> ```shell jpeginfo -c -i Borago_officinalis_2015-11-18.JPG Borago_officinalis_2015-11-18.JPG 4000 x 3000 24bit N Exif,XMP,MPF Huffman 1907802 OK ``` Much thanks in advance!!