Confira essa resposta anterior de superusuário: "Programa para ler dados de gráficos digitalizados" .
Veja também a página da Wikipedia em Convertendo gráficos digitalizados em dados . Abaixo está a lista de softwares nessa página:
DataThief III is Java standalone software to digitize plots.
Engauge Digitizer is an open source digitizing software available for Linux and Windows. Latest release in 2007.
Plot Digitizer is an open source Java program for digitizing scanned plots. It is available for a number of platforms. Actively developed as of November 2011.
g3data is open source graph digitizer based on GTK+. Last release in 2011.
Silk Scientific, Inc. www.silkscientific.com offers proprietary graph digitizing software such as Un-scan-it
DigitizeIt is a proprietary digitizer.
Graphics software FindGraph from UNIPHYZ Lab contains digitizing capability.
General graphics package ORIGIN (proprietary) includes tools for digitization.
GetData Graph Digitizer is a proprietary standalone software to digitize plots.
Dagra, a proprietary program for Microsoft Windows, uses Bezier curves to digitize graphs.
OmniGraphSketcher, a proprietary Macintosh application, allows interactive point selection from graphics displayed on screen (via a transparent window).
XYit Image Digitizer (proprietary) from Geomatix, for graphs, maps and charts
WebPlotDigitizer is a good online graph digitizing tool.