NO.
For the Tapas app's case, you can view the comic through the app but are not allowed to screenshots of comic through the app . There's probably something related to DRM and the term-and-conditions for what you can do and can not do in the app.
There are other ways to read comics, where you can take screenshot or picture -- like through a web-browser on a computer or on printed-paper if available at your local library, etc.