Welcome to the community greengold. [excited]
Actually Photoshop is THE program used for this type of purpose.
Open the left half of the bridge, then open the right half.
Right-click on the TITLE BAR of the right half photo and choose "Image Size". Take note of the width of the photo. Make sure you also take note of whether the measurement is in inches, cm, or pixels.
Go back to the left half photo and right-click on its TITLE BAR. Choose "Canvas Size". Change the measurement type if need be, to match the other photo. Then increase the Width setting to include the width of the right half photo. You're going to be bringing that photo into this document, so you need to increase the width so it'll fit properly.
Before clicking OK, take a look at the small grid of buttons at the bottom of the window. ( see 1st image below ) These are for telling PS how you'd like your current content to be positioned once the extra space has been added to the canvas. In this case, we want the left half of the bridge to be on the left, so click that button -- the left middle button. (2nd button down on the left side)
Now click OK.
Now go to the right half photo and select All (Ctrl+A). Then Ctrl+C to copy. Now return to the left half photo again and press Ctrl+P to paste. Select All again and choose the MOVE tool from the Toolbar. Now look within the Options Bar atop your work area. You should see some alignment function buttons. ( see 2nd image below ) Choose the one that has all of the squares on the right side, stuck to a solid vertical line.
You should now be seeing the 2 photos together as one. If there is any gap between them ( there shouldn't be though ) Just click the right half photo to make it active, then select the MOVE tool and tap your left arrow key enough times to close the gap.
Any questions, just ask.