The best size is approximately 576 pixels in height and 100 pixels in width. Note: Images that are smaller than 576 pixels tall by 100 pixels wide will tile. Read further to know how to edit the file size with the recommended specifications.
If you use Paint, right click on the image and select to open in Paint. The image opens in paint. Go to the top menu bar and select the option to resize the picture. Tick the button for giving the size in pixels and uncheck the box for percentage. Uncheck the box that says to maintain the aspect ratio. Now, manually type the height and width values in pixels in the columns given and apply the effect. Save the new image in .gif or .jpeg format. This is done by going to the File<Save As option and giving the file name and extension as instructed.
You can also edit the size of the image file in other image viewer applications with the same process. You have to open the image in the said application and go to edit option. There will be menu bar to change or resize the image specifications. It is important to follow the size specifications so that you can upload your design with the required compatibility into the database.
This application will accept GIFs and JPEGs only and will not accept any images larger than 500 KB.