Hi and welcome to the forums
Most transfers are fairly soft now compared to the old school ones

you could do this easily if you are doing light color shirts, with a paper such
as jet pro soft stretch, an inkjet printer and a heat press. That is probably what I would
do if I were wanting to put pictures/photos on a shirt at an event, and I was using transfers.
If you are selling certain transfers premade, you can either get stock plastitol transfers, or have
them made with your own images prior to the event. Plastitol transfers are screen printed
so they are like screen printed shirts, but you apply them as you use them.