It’s rather new, but it’s getting popular fast: Bitstrips on Facebook.
The next time Bitstrips posts an image on someone’s behalf, move your mouse pointer over the top right corner of the post (just below the thin line separating the post from the one above). This will display a small button with a down pointing symbol. Click it to display a menu. Then select “Hide all from Bitstrips“.
You’ll have to answer two questions about why you don’t want to see it (both can be answered by clicking an option, so it will be done in a snap). This then will be the last you see from Bitstrips.
By the way: You can use the same method to hide posts from other apps your FB friends are using.
Unfortunately this doesn’t guard you against Bitstrips posted on the timelines of others.
Also Bitstrips users may still be able to post you images from that app, om their own.