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Is there a way for me to easily find and mark with a dot the center point of an image/photo?

I have no specific requirements for what software to do this (though I currently only have access to Gimp and Photoshop CS3, I am willing to install others).

I prefer solutions that allow the following (but they're not hard requirements):

(1) I prefer it to work on Windows, Macs, and Linux machines.

(2) I prefer to mark the center point "non-destructively", i.e. I still like to have the original image without any marks (maybe through layers?).

Thanks!

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up vote 1 down vote accepted

Install ImageMagick. It has packages for Windows, OS X and Linux, although you may have to build from source using MacPorts for OS X.

Once installed, at a comand prompt type: composite -gravity center small-center-image.jpg original-image.jpg: new-image.jpg

This will overlay the small-center-image.jpg over the original image and save it under a new filename. Further examples of this particular command can be found here.

This is just barely scratching the surface of what the ImageMagick toolset can do. A full set of HTML documentation pages will be available on your computer with the install of the package.

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I installed ImageMagick via MacPorts in OS X, but got the error "composite: no decode delegate for this image format". What does that mean? – hpy Apr 12 '11 at 20:56
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The documentation is apparently wrong - remove the colon after the orignal-image name. Then it should work. Refer to this imagemagick.org/discourse-server/viewtopic.php?f=1&t=18515 for details. – Scott McKinney Apr 14 '11 at 0:19
    
Ah yes that did it, and the compositing works fine now. Thank you for the answer! – hpy Apr 14 '11 at 18:39

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