How to Highlight Found Keywords or Patterns in Search Results

Visual feedback—highlighting found terms or patterns—greatly improves usability and review speed in compliance, discovery, and document review apps. Aspose.OCR Image Text Finder for .NET supports programmatic highlighting of OCR search results.

Real-World Problem

Users reviewing large batches of search results need visual cues to quickly spot matched terms/patterns in images. Manual markup is slow and error-prone.

Solution Overview

Detect matches, retrieve their bounding box coordinates using OCR region data, and programmatically overlay highlights/annotations for end users.

Prerequisites

1. Visual Studio 2019 or later
2. .NET 6.0 or later
3. Aspose.OCR for .NET from NuGet
4. System.Drawing.Common or SkiaSharp for overlay

PM> Install-Package Aspose.OCR
PM> Install-Package System.Drawing.Common

Step-by-Step Implementation

using Aspose.OCR;
using System.Drawing;

string imgFile = "document.png";
string keyword = "Confidential";
RecognitionSettings settings = new RecognitionSettings();
settings.Language = Language.English;
AsposeOcr ocr = new AsposeOcr();
List<RecognitionResult> results = ocr.Recognize(new OcrInput(InputType.SingleImage) { imgFile }, settings);
foreach (var block in results[0].TextBlocks)
{
    if (block.Text.Contains(keyword))
    {
        // Proceed to highlight this region (block.Rect)
    }
}

using (Bitmap bmp = new Bitmap(imgFile))
using (Graphics g = Graphics.FromImage(bmp))
{
    foreach (var block in results[0].TextBlocks)
    {
        if (block.Text.Contains(keyword))
        {
            var rect = block.Rect; // Rectangle coordinates from OCR
            g.DrawRectangle(new Pen(Color.Red, 3), rect.X, rect.Y, rect.Width, rect.Height);
        }
    }
    bmp.Save($"highlighted_{Path.GetFileName(imgFile)}");
}

using Aspose.OCR;
using System;
using System.Collections.Generic;
using System.Drawing;
using System.IO;

class Program
{
    static void Main(string[] args)
    {
        string imgFile = "document.png";
        string keyword = "Confidential";
        RecognitionSettings settings = new RecognitionSettings();
        settings.Language = Language.English;
        AsposeOcr ocr = new AsposeOcr();
        List<RecognitionResult> results = ocr.Recognize(new OcrInput(InputType.SingleImage) { imgFile }, settings);
        using (Bitmap bmp = new Bitmap(imgFile))
        using (Graphics g = Graphics.FromImage(bmp))
        {
            foreach (var block in results[0].TextBlocks)
            {
                if (block.Text.Contains(keyword))
                {
                    var rect = block.Rect;
                    g.DrawRectangle(new Pen(Color.Red, 3), rect.X, rect.Y, rect.Width, rect.Height);
                }
            }
            bmp.Save($"highlighted_{Path.GetFileName(imgFile)}");
        }
    }
}

Use Cases and Applications

Legal & Compliance Review

Highlight found terms in scanned contracts for fast approval.

Digital Asset Management

Visually annotate images for easier retrieval and review.

E-Discovery & Audit

Mark and present evidence for compliance, audit, or litigation.

Common Challenges and Solutions

Challenge 1: Overlapping/Complex Patterns

Solution: Use different highlight styles/colors for clarity.

Challenge 2: OCR Region Precision

Solution: Validate coordinates and tune OCR/image resolution.

Challenge 3: Batch/Automated Highlighting

Solution: Optimize rendering and parallelize overlay for large sets.

Performance Considerations

• Overlay rendering is fast but can bottleneck at scale—use async where possible
• Batch process and log highlighted files

Best Practices

1. Validate highlights visually before publishing to end users
2. Secure all images and highlight overlays for privacy
3. Regularly test with diverse file types and patterns
4. Offer toggle/undo for interactive UIs

Advanced Scenarios

Scenario 1: Custom Annotations/Text Labels

Display keyword text, severity, or custom notes on overlays.

Scenario 2: Export to PDF or Multi-Format Output

Render highlights on PDF or image sets for sharing/review.

Conclusion

Aspose.OCR Image Text Finder for .NET makes it easy to programmatically highlight and annotate found terms in images—improving accuracy and review speed for compliance, discovery, and business workflows.

See Aspose.OCR for .NET API Reference for more advanced search and annotation features.