NOTE: Recent versions of Inkscape have replaced the "Effects" menu with "Extensions". The perspective extension is in Extensions ‣ Modify Path ‣ Perspective.
In my testing you have to select the object to modify first, followed by the perspective path.
When using Inkscape 0.92 or later, it's generally easier to use the "Perspective/Envelope" live path effect. See part 69 of my tutorial series in Full Circle Magazine issue #129 for more details: http://fullcirclemagazine.org/issue-129/
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A few years ago heathenX and Richard Querin created a series of tutorial videos for Inkscape, a Free and Open Source vector graphics program that can be downloaded from http://inkscape.org
The original heathenX website no longer exists, however I have obtained a backup of all their tutorial videos and will be uploading them to Youtube over the coming months. All the videos are licensed under a Creative Commons Attribution 4.0 International (CC BY 4.0) license
(https://creativecommons.org/licenses/.... You are welcome to share and modify them in any way, but if you do so they must remain
under the same license, and must be attributed to Richard Querin and heathenX.
If you are the sort of person who prefers lengthy, written tutorials, rather than a Youtube video, my own series of Inkscape tutorials for Full Circle Magazine can be downloaded for free from https://fullcirclemagazine.org/inksca...