What kind of pictures does the ti84 support (Jpeg,Png,Bitmap,Tiff)?
It doesn't support any of those natively, but if you use TI-Connect, I believe you can save (possibly import) bitmaps.
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If you are trying to transfer a pic from computer to calc, I'm no help there. But if you just want to know what type of pc ti supports, connect your calc to your computer and open ti connect: ti device explorer. There is a "take a screen shot" option at the top of the screen, click on it and it will save whatever is displayed on your calc at the time. Look in the directory holding the picture, view its details and locate the file type.