Image formats not generating picture descriptions, only OCR text extraction

When converting images using Docling, the library **does not generate picture descriptions for image formats**. It only performs OCR text extraction when text is present in the image. The `pictures=[]` array remains empty for all images, regardless of whether they contain text or not, making it impossible to retrieve any visual content descriptions.

**However**, if the **same image is embedded in a PDF file**, Docling correctly generates picture descriptions and populates the `pictures` array. This inconsistency suggests that the image processing pipeline behaves differently for standalone image formats (PNG, JPG) versus images within PDF documents.

> _This image features a close-up of an adorable ginger tabby kitten with bright, curious blue eyes. The kitten has a soft, orange-striped coat and is gazing up with an expression of innocence and wonder. The background is softly blurred, drawing attention to the kitten’s sweet and delicate features._

### Steps to reproduce
1. Set up Docling with the following configuration:
```python
InputFormat.IMAGE: ImageFormatOption(pipeline_options=pipeline_options)
# or InputFormat.PDF: PdfFormatOption(pipeline_options=pipeline_options),

def _build_full_pipeline_options(self) -> PdfPipelineOptions:
"""Build the full/accurate PdfPipelineOptions configuration.

Includes OCR, table structure, formula/code enrichment and picture description.
"""
pipeline_options = PdfPipelineOptions()
pipeline_options.do_ocr = True
pipeline_options.do_table_structure = True
pipeline_options.do_formula_enrichment = True
pipeline_options.do_code_enrichment = True
pipeline_options.generate_picture_images = True
pipeline_options.enable_remote_services = True
pipeline_options.do_picture_description = True
pipeline_options.picture_description_options = self._picture_description_options # OpenAI
return pipeline_options
```

2. Convert two versions of the same image:
- **Image with text** (`pussInBoots.png`): Contains the text "am Puss in Boots"
- **Image without text** (`pussInBoots_no_text.png`): Same image with text removed

```python
result = converter.convert(image_file)
markdown_content = result.document.export_to_markdown(image_mode=ImageRefMode.REFERENCED)
```

3. Inspect the resulting `DoclingDocument` objects:
```python
print(result.document.pictures) # Returns empty list [] for both images
print(result.document.texts) # Returns text only for image with text
```

4. Convert the same image embedded in a PDF file and observe that picture descriptions are correctly generated.

**Expected behavior:** The `pictures` array should contain picture items with descriptions of the visual content (e.g., "A cat wearing boots and a hat") for all images, regardless of whether text is present and regardless of whether the image is standalone or embedded in a PDF.

**Actual behavior:**
- For **standalone images with text**: Only OCR text extraction occurs (`texts=['am Puss in Boots']`), no picture description generated (`pictures=[]`)
- For **standalone images without text**: No content extracted at all (`texts=[]`, `pictures=[]`)
- For **images in PDF files**: Picture descriptions are correctly generated and populate the `pictures` array
- The image processing pipeline appears to focus exclusively on text extraction for standalone image formats and does not generate visual content descriptions

**Example output for image WITH text:**

`python schema_name='DoclingDocument' version='1.7.0' name='pussInBoots' texts=[TextItem(..., orig='am Puss in Boots', text='am Puss in Boots', ...)] pictures=[] # Empty! No image description generated`

**Example output for image WITHOUT text:**
`python schema_name='DoclingDocument' version='1.7.0' name='pussInBoots_no_text' texts=[] # Empty, as expected pictures=[] # Empty! Should contain image description`

### Docling version
```
Docling version: 2.55.1
Docling Core version: 2.48.4
Docling IBM Models version: 3.9.1
Docling Parse version: 4.5.0
```

### Python version
```
Python 3.13.7
```

### Attachments
[images.zip](https://github.com/user-attachments/files/22866808/images.zip)

### Logs

```python
schema_name='DoclingDocument' version='1.7.0' name='pussInBoots' origin=DocumentOrigin(mimetype='application/pdf', binary_hash=16517824524666051744, filename='pussInBoots.png', uri=None) furniture=GroupItem(self_ref='#/furniture', parent=None, children=[], content_layer=, name='_root_', label=) body=GroupItem(self_ref='#/body', parent=None, children=[RefItem(cref='#/texts/0')], content_layer=, name='_root_', label=) groups=[] texts=[TextItem(self_ref='#/texts/0', parent=RefItem(cref='#/body'), children=[], content_layer=, label=, prov=[ProvenanceItem(page_no=1, bbox=BoundingBox(l=158.33333333333334, t=1115.6666666666667, r=824.6666666666666, b=1034.6666666666667, coord_origin=), charspan=(0, 16))], orig='am Puss in Boots', text='am Puss in Boots', formatting=None, hyperlink=None)] pictures=[] tables=[] key_value_items=[] form_items=[] pages={1: PageItem(size=Size(width=1000.0, height=1250.0), image=None, page_no=1)}
```

Compare the InputFormat.IMAGE/ImageFormatOption path with InputFormat.PDF/PdfFormatOption, starting at converter.convert and the configured PdfPipelineOptions. Trace why standalone images reach OCR but not picture-description processing, then verify both attached image cases and PDF behavior. Done means standalone images populate pictures with visual descriptions while preserving OCR.

Written by the indexing model from the issue text.