TssTransparentBitmap is derived from TGraphicControl.

Bitmap PropertyPublished TBitmap
The bitmap to display. The transparent colour is the colour of the bottom-left pixel.
PlainParent PropertyPublished boolean
Whether the background behind the bitmap is a plain solid colour. If the background is plain then a quicker method of drawing the bitmap (BrushCopy) can be used, otherwise a slower method is needed to preserve the background. If in doubt, set this to false.