For geo-referencing of files in *.jpg or *.jpeg format, a file of the type *.jgw has to be created. For this, the extreme coordinates of the model or the model boundary xmin/ymin and xmax/ymax in world coordinates (usually Gauss-Krüger coordinates) and the display size of the Schlieren illustration in pixels (sizeX/sizeY) is needed.
The coordinates are for example determined using the menu item View 
Show coordinates. The extension of the Schlieren illustration can be seen in the output file *.scr, after the data was exported for the Schlieren illustration (File Export Schlieren illustration). The file can be opened with any editor. The line "size" refers to the pixel size of the plot.
If the required numbers are determined, an ASCII file is created with an editor. It contains the following numbers (upper suspension point) and scaling:
1st line: (xmax-xmin)/sizeX
2nd line: 0.0
3rd line: 0.0
4th line: (ymin-ymax)/sizeY
5th line: xmin
6th line: ymax
The file will be renamed by the name of the Schlieren image with the extension *.jwg. This geo referencing file is automatically evaluated when opening the Schlieren image with SPRING.
Tip: By increasing the pixel value in the Input window of the data export the resolution increases as well.
In the current SPRING-release, the Schlieren images are automatically geo referenced in horizontal and 3D models (only when representing defined layers).