PureBasic allows you to create image plugins through a special type of user libraries, which have the following common characteristics:
Two exported functions which registers the encoder and the decoder plugins.
Within that functions, the plugin is registered using a function exported by the ImagePlugin library. A structure with the addresses to four functions must be passed using that function.
The current implementation of ImagePlugins has changed: It is now an include file much like the TB_Debugger include file. (in the Helper Libraries subfolder of your TailBite install folder)
You should look at and copy ImageDecoderFake and/or FakeImageEncoder in the Samples folder in you TailBite install folder. You should only change the names of the ProcedureDLLs (plus the globals defined in the Init function) and the content of the Procedures (not the ProcedureDLLs). These samples are a very easy to understand skeleton, they have most of the comments found in their counterpart C examples in the PB SDK.
They are also x64 compatable.