Using a photo editing software, like Photoshop, write information about the first day of school on the chalkboard background using one of the handwriting fonts. Use white or contrasting colored letters. Information you can write includes the date, the grade/school year the child is beginning, the teacher's name, favorite color, book, or movie, etc. Leave some space around the writing so that you can cut the chalkboard as needed without cutting of the wording.
Print out the chalkboard design just slightly larger than the opening of the frame or mini chalkboard (around 1mm larger on each side). This will allow you to cut the frame to the exact size needed without leaving any white space.
If your frame will allow it, you can cut the paper slightly larger than the opening of the frame and tuck the edges underneath. If not, carefully cut the chalkboard printable to the exact size of the opening.
Use double-sided tape to temporarily tape the printable in place on top of the glass of the frame or on top of the chalkboard. Tuck the edges of the paper under the frame if you are able.
Have your child hold the chalkboard sign while you take photos on the first day of school!
Notes
Consider getting at least one photo of the child standing each year so that you can compare how they grow. Have the child wear and/or stand by things that they might like to remember. This includes things like that year's backpack or snack bag. If you don't have any photo editing software on your computer, you can use online photo editors like Pixlr.