This page lists thumbnails of noteworthy images I've contributed to Wikipedia. If you find them useful for Wikipedia articles you're editing, by all means link them or make prettier derivatives of them. Unless otherwise noted, they're licensed under the Creative Commons share-alike license.
This image illustrates the forward light cones of points along the worldlines of objects moving near a black hole. In case 1), the light cones are not substantially affected by the hole's gravity. In case 2), the light cones are tilted towards the black hole, but emitted light can still escape. In case 3), as the infalling object approaches the event horizon, the forward light cone of the object tilts so that its outer edge is aligned with the horizon. Light emitted at this event takes an arbitrarily long time to escape the hole. In case 4), the infalling object is within the event horizon, and all parts of the light cone point intwards. Moving towards the singularity is inevitable.
This image illustrates the exchange of information with an object falling into a black hole. An observer, O, sends timestamped radar pulses to a reflective infalling object P, as the object approaches the black hole's event horizon H. When P is far from the hole, the radar pulse is returned in the expected amount of time (pulse 1). When the object is close to the horizon, the return pulse is delayed by an arbitrarily large amount of time (pulse 2). Pulses emitted after pulse 2 are not returned (pulse 3), even though an image of the object is observed at the time the pulse is emitted (when pulse 3 is emitted, the observer has seen pulse 1 returned and is waiting for the return of pulse 2).
This image illustrates a spacetime diagram containing the world line of a uniformly accelerating particle, P, and the light cone of an event, E. The event's light cone never intersects the world line of the particle; the event is therefore beyond an event horizon perceived in the particle's accelerating reference frame.
This figure illustrates world lines drawn in a) positively curved spacetime and b) negatively curved spacetime. In positively curved spacetime, for an initial world line with an event (point) that isn't on the world line, any new world line that passes through the event will intersect the original world line ("parallel" world lines aren't possible). In negatively curved spacetime, for an initial world line with an event (point) that isn't on the world line, more than one distinct world line can be drawn through the event, without any of these new world lines intersecting the original world line. In flat spacetime, exactly one "parallel" world line can be drawn.
This figure illustrates objects moving through a region of positive spacetime curvature (a borehole through the Earth). The world lines in the spacetime diagram are parallel at points B and D, but intersect at points A and C. This intersection of parallel lines indicates that spacetime is positively curved.
This figure illustrates objects moving through a region of negative spacetime curvature (falling towards the Earth). The leftmost animation shows the object cluster falling, while the middle animation shows the components of the cluster moving in response to tidal forces. The world lines are plotted with position measured with respect to the blue test object (its position is treated as constant), to show tidal effects. There are two world lines that pass through point X on the spacetime diagram, and none of these intersect the worldline of the blue test object. This drawing of multiple lines that don't intersect the blue world line indicates that spacetime is negatively curved.
I'm lucky enough to have the Toronto Reference Library on my doorstep, which specializes in very old published works. As a result, I've contributed scans of works whose copyright has expired. Copyright information is given in the text associated with the image files.