Picture tubes are graphic images with no background. They are used combined with other image elements to produce comment graphics for use on social networks and as personal signature tags. Tagging is a popular passtime for many very creative people and I find it a pleasure to offer my illustrations for use in these wonderful creations.
The format I use is a transparent PNG file which can be dropped into any graphics application which supports layers, such as Photoshop or Paint Shop Pro. (Why PNG?)
A copyright credit is included in the image but you are free to lasso it and move it about as you please, but please do include it and use in accordance with the provisions specified in my Creative Commons license, the most important being you may not use for commercial purposes.
I share my illustrations as free-to-use tubes via Twitter on a weekly basis; catch me there to see what is available.