If you still have the installer and want to use it for nostalgic purposes, the software may run in "Trial Mode," which typically allows for a limited number of collages (usually 30 days or a set number of saves) but will often apply a watermark to the final image.
If you are looking for a "25-character product key" for this software today, you will likely encounter the following issues: microsoft research autocollage 2008 25character product key
Since you cannot reliably activate AutoCollage 2008 in the current software ecosystem, you might consider these modern, supported alternatives that perform similar "intelligent" blending: If you still have the installer and want
Microsoft stopped selling and supporting AutoCollage years ago. you might consider these modern