Log on to the different comic printing services and see what the specifications are for pages for a printed comic. (See Resources) Most standard comics are 7 inches by 10 1/2 inches, with a "live area" set at 6 1/4 inches and 9 3/4 inches. All images must be placed within the live area of the comic book page. Most printing websites have a template you can download. It is advisable to download the template.
Open up the template you downloaded from the printing service website in Adobe Photoshop or other art program and open up the first page of your webcomic. Change the image size of your webcomic to fit within the margins of the "live area" on the template. Copy and paste the page of your webcomic into the template. Fill the background of the template with either white or black, depending on the color of your webcomic page. Save the new page as a TIF file with the page number as the name.
Repeat Step 2 for each page of your comic.
Create an account with a comic book printer. (See Resources) Fill out the form for a new comic project.
Find the folder where you saved all the TIF files on your computer. Open the folder and select all the TIF files you created from the previous section. Right-click on the selected files and click "Add to Archive." Create a ZIP file which will save all the files as a single compressed file. Save the file on your computer in a folder that you can easily find.
Send the ZIP file that you created to the printing company. Depending on the printer, you will either upload the file directly on the company's website, or send it through a file hosting service such as SendSpace.com.