Image Text Finder
How to Compare Text Across Document Versions Using .NET

How to Compare Text Across Document Versions Using .NET

Comparing text between different scanned versions of contracts, forms, or business documents is critical for legal review and compliance. Aspose.OCR Image Text Finder for .NET streamlines the process by automatically extracting and comparing text from multiple images.

Real-World Problem

Manual review of version changes is slow, prone to human error, and not scalable—especially when handling many document revisions or legal contracts.

Solution Overview

Automate the comparison by extracting text from two or more scanned images, then using diff logic to highlight and log textual changes.

Prerequisites

  1. Visual Studio 2019 or later
  2. .NET 6.0 or later (or .NET Framework 4.6.2+)
  3. Aspose.OCR for .NET from NuGet
PM> Install-Package Aspose.OCR

Step-by-Step Implementation

Step 1: Prepare Document Versions 

string original = "contract_v1.png";
string revised = "contract_v2.png";

Step 2: Recognize and Extract Text from Images 

RecognitionSettings settings = new RecognitionSettings();
settings.Language = Language.English;
AsposeOcr ocr = new AsposeOcr();
string originalText = ocr.Recognize(new OcrInput(InputType.SingleImage) { original }, settings)[0].RecognitionText;
string revisedText = ocr.Recognize(new OcrInput(InputType.SingleImage) { revised }, settings)[0].RecognitionText;

Step 3: Compare Text and Highlight Differences

Use a text diff/compare library (e.g., DiffPlex, built-in logic) to spot differences:

using DiffPlex;
using DiffPlex.DiffBuilder;
using DiffPlex.DiffBuilder.Model;

var diffBuilder = new InlineDiffBuilder(new Differ());
var diff = diffBuilder.BuildDiffModel(originalText, revisedText);
foreach (var line in diff.Lines)
{
    if (line.Type != ChangeType.Unchanged)
        Console.WriteLine($"{line.Type}: {line.Text}");
}

Step 4: Log and Export Comparison Results

  • Save changes to CSV, log file, or human-readable diff report
// Example: Write all changes to a report
File.AppendAllText("text_diff_report.txt", $"{line.Type}: {line.Text}\n");

Step 5: Batch or Automate Version Control

  • Compare all versions in a folder, automate as needed

Step 6: Complete Example 

using Aspose.OCR;
using DiffPlex;
using DiffPlex.DiffBuilder;
using DiffPlex.DiffBuilder.Model;
using System;
using System.IO;

class Program
{
    static void Main(string[] args)
    {
        string original = "contract_v1.png";
        string revised = "contract_v2.png";
        RecognitionSettings settings = new RecognitionSettings();
        settings.Language = Language.English;
        AsposeOcr ocr = new AsposeOcr();
        string originalText = ocr.Recognize(new OcrInput(InputType.SingleImage) { original }, settings)[0].RecognitionText;
        string revisedText = ocr.Recognize(new OcrInput(InputType.SingleImage) { revised }, settings)[0].RecognitionText;
        var diffBuilder = new InlineDiffBuilder(new Differ());
        var diff = diffBuilder.BuildDiffModel(originalText, revisedText);
        foreach (var line in diff.Lines)
        {
            if (line.Type != ChangeType.Unchanged)
                File.AppendAllText("text_diff_report.txt", $"{line.Type}: {line.Text}\n");
        }
    }
}

Use Cases and Applications

Legal and Compliance Review

Quickly spot changes in scanned contracts, policies, or agreements.

Business Process Auditing

Detect unauthorized or unapproved edits in digital archives.

Document Management Automation

Maintain a complete audit trail of all changes across scanned document versions.

Common Challenges and Solutions

Challenge 1: Minor Formatting or OCR Errors

Solution: Tune settings, run secondary manual review on flagged changes.

Challenge 2: Large Document Sets

Solution: Automate and parallelize, log all results for efficient auditing.

Challenge 3: False Positives/Negatives

Solution: Refine diff algorithm, validate output with real-world samples.

Performance Considerations

  • Diff logic may be slow on large documents—monitor and optimize
  • Store all diff reports securely for compliance
  • Use robust OCR settings for best recognition

Best Practices

  1. Use the same OCR and scan settings across all versions
  2. Validate diffs on critical/high-risk documents
  3. Log and back up all reports
  4. Automate regular version comparison for key documents

Advanced Scenarios

Scenario 1: Highlight Differences in Visual Output

Generate annotated PDFs/images that highlight detected text changes for legal teams.

Scenario 2: Automate Notification on Critical Changes

Send alert/email if important legal clause is added/removed.

Conclusion

Aspose.OCR Image Text Finder for .NET enables automated, scalable, and auditable document version comparison—empowering legal, business, and compliance teams to detect critical changes in scanned files.

For more advanced comparison workflows, see Aspose.OCR for .NET API Reference .

 English