Turn my image into a brush

Can anyone help either with instructions - or with links to documents/videos.  I can't find any that does exactly what I want them to do.  They take me about 90% of the way there, but I need help with the final 10%. 

WHAT I HAVE CREATED

I have a full colour image of a butterfly.  I can turn it into a stamp brush which always points in the same direction - and that's fine for one of the uses for this brush.  I have also created a similar brush (for a butterfly for which I can set to the colour I want, and it applies that colour to the whole butterfly).  I also  vary the size and direction by using both Size Jitter and Angle Jitter.  Again, this accomplished what I wanted at the time.

WHAT I WANT TO CREATE NOW

I would like an amalgum of the two items above.  I'd like to create a brush from the full colour butterfly, which I can resize each time I use it.  I also want it to change size and directions (which I thought I could use using similar jitter settings as above).  However, I can't seem to achieve this.  When I use the size jitter rather than resizing the butterfly (which it did when I created the single colour butterfly)  it only shows part of it eg if its small it shows just the body, as it gets bigger it also shows parts of the wings. Also, the jitter angle doesn't seem to work.

As I say, I think I'm about 90% of the way there - but just can't work out the last 10%.  So help would be gratefully accepted - many thanks in advance.