What is Blender's maximum render (not scene) size? Like in either MegaPixels or a pixel length x width dimension. On my side it seems to be locked at 22000 pixels. Using the Cycles render engine to render TIFFs.
The maximum render size is computer dependent, and therefore also scene dependent. In Cycles, it is further constrained by GPU RAM if you are using GPU rendering; my experience is that my Titan X is fast, but easy to overwhelm. Note that having multiple GPU cards makes rendering faster, but each card must still be able to get the image into GPU RAM (as I understand it based on StackExchange info).
We sometimes render images bigger than 30K in one or both dimensions. The easiest way to do so is certainly to send off your image to a farm that supports tiling. Your images will be broken into segments and rendered individually, then recomposited. Depending upon the farm, some features (compositor, render border) may be disabled, and this approach is less useful with some global illumination schemes.
I suspect a python ninja could create a plug-in to do this, allowing the same approach on your desktop... although another advantage of a farm is that you do not have to sit through a 1.5 billion pixel render.
That is one of two wall images, each more than 50 feet tall. Done in Blender (although in multiple scene files).
The maximum rendered image size will depend on how much RAM you have, with the scene size adding to the RAM needed.
Up to v2.66 you can enter a resolution up to a maximum size of 10,000 in both directions and from v2.67 that increased to 65,536 and you can then multiply that with a scale up to 32,767% which leads to a maximum of 21,474,181 in either direction (or 3,270,000 before 2.67).
Given a resolution of 65536x65536x100% blender allocates 98G. While it tries to start rendering I don't have enough RAM for it to get far in any reasonable amount of time.
I don't think it is locked to 22000. I have personally rendered image 43000 + pixels in one dimension.
Biggest picture i rendered was around 30000x10000. All those was in multi layer EXR and .png
The bigger problem i found is saving those images. Blender crashed on me when i saved images this large. I have to render it in parts and compose whole image after.