What I have started to do is use a simple template in a Google Doc file. I create a table of 4 rows, the first and last row are 1cm high and the two center rows are 3cm high. Column width is 10cm. That gives 9 columns to a row and is a good size for Human scale minis. I usually type in the name of the character or monster in the 1st and 4th rows to identify them easily. Then, find a suitable image – for personal use you can grab a whole raft of images from the internet for a wide variety of characters and monsters. Paste the image into the two middle rows of a column, scale to fit. The upper row (row 2) will be the back of the image. I tend to select the row and set the background image to grey which will usually give a border around the image marking it as the back. I rotate the image in row 2 by 180 degrees as well.