My version of creating an occlusion card is to take a screenshot using Windows snip, open the image on my computer, then draw over sections of the image. The front of my card is the obscured image; the back is the full image. This way, I can create a card every 20-30 seconds (and deciding which parts to occlude is a good form of revision in itself).
I don’t know how often you do that, but if it’s sufficiently frequent, it might be quicker to do with the tool ShareX (free, open source, Windows only), which can do all of the following in the minimum conceivable number of clicks: a) taking the screenshot, b) editing the screenshot in a built-in image editor, c) copying the edited image to your clipboard (or uploading it to an image hoster and copying the URL to your clipboard or something).
I don’t know how often you do that, but if it’s sufficiently frequent, it might be quicker to do with the tool ShareX (free, open source, Windows only), which can do all of the following in the minimum conceivable number of clicks: a) taking the screenshot, b) editing the screenshot in a built-in image editor, c) copying the edited image to your clipboard (or uploading it to an image hoster and copying the URL to your clipboard or something).