diff --git a/cmd/fastgallery/main.go b/cmd/fastgallery/main.go
index 60f338b..968e440 100644
--- a/cmd/fastgallery/main.go
+++ b/cmd/fastgallery/main.go
@@ -28,6 +28,10 @@ var assets embed.FS
 // Define global exit function, so unit tests can override this
 var exit = os.Exit
 
+// Define global state for slice of WIP transformation jobs, used by signalHandler()
+var wipJobs = make(map[string]transformationJob)
+var wipJobMutex = sync.Mutex{}
+
 // configuration state is stored in this struct
 type configuration struct {
 	files struct {
@@ -76,7 +80,8 @@ func initializeConfig() (config configuration) {
 	config.media.fullsizeMaxHeight = 1080
 	config.media.videoMaxSize = 640
 
-	config.concurrency = 8
+	// TODO adjust based on cores
+	config.concurrency = 4
 
 	return config
 }
@@ -869,8 +874,17 @@ func getGalleryFilenames(sourceFilename string, config configuration) (thumbnail
 	return
 }
 
+// transformFile takes a transformation job (an image or video) and creates a thumbnail, full-size
+// image and a copy of the original
 func transformFile(thisJob transformationJob, progressBar *pb.ProgressBar, config configuration) {
-	// TODO add ctrl-C support, signal intercept
+	// Before we begin work, add all work-in-progress files to wipSlice
+	// In case the program is killed before we're finished, signalHandler() deletes all the wip files.
+	// This way, no half-finished files will stay on the hard drive
+	wipJobMutex.Lock()
+	wipJobs[thisJob.sourceFilepath] = thisJob
+	wipJobMutex.Unlock()
+
+	// Do the actual transformation and increment the progress bar
 	if isImageFile(thisJob.filename) {
 		transformImage(thisJob.sourceFilepath, thisJob.fullsizeFilepath, thisJob.thumbnailFilepath, config)
 	} else if isVideoFile(thisJob.filename) {
@@ -881,6 +895,10 @@ func transformFile(thisJob transformationJob, progressBar *pb.ProgressBar, confi
 	}
 	createOriginal(thisJob.sourceFilepath, thisJob.originalFilepath)
 	progressBar.Increment()
+
+	wipJobMutex.Lock()
+	delete(wipJobs, thisJob.sourceFilepath)
+	wipJobMutex.Unlock()
 }
 
 // This is the main concurrent goroutine that takes care of the parallelisation. A big bunch of them
@@ -995,6 +1013,13 @@ func setupSignalHandler() {
 func signalHandler(signalChan chan os.Signal) {
 	<-signalChan
 	log.Println("Ctrl-C received, cleaning up and aborting...")
+	wipJobMutex.Lock()
+	for _, job := range wipJobs {
+		fmt.Println("cleaning:", job.filename)
+		os.Remove(job.thumbnailFilepath)
+		os.Remove(job.fullsizeFilepath)
+		os.Remove(job.originalFilepath)
+	}
 	exit(0)
 }
 
diff --git a/testing/gallery/_fullsize/2021-01-02 23.51.34.mp4 b/testing/gallery/_fullsize/2021-01-02 23.51.34.mp4
deleted file mode 100644
index f9a0926..0000000
Binary files a/testing/gallery/_fullsize/2021-01-02 23.51.34.mp4 and /dev/null differ
diff --git a/testing/gallery/_original/2021-01-02 23.51.34.mp4 b/testing/gallery/_original/2021-01-02 23.51.34.mp4
deleted file mode 120000
index c017102..0000000
--- a/testing/gallery/_original/2021-01-02 23.51.34.mp4	
+++ /dev/null
@@ -1 +0,0 @@
-/home/toni/go/src/github.com/tonimelisma/fastgallery/testing/source/2021-01-02 23.51.34.mp4
\ No newline at end of file
diff --git a/testing/gallery/_thumbnail/2021-01-02 23.51.34.jpg b/testing/gallery/_thumbnail/2021-01-02 23.51.34.jpg
deleted file mode 100644
index 9e43820..0000000
Binary files a/testing/gallery/_thumbnail/2021-01-02 23.51.34.jpg and /dev/null differ
diff --git a/testing/gallery/index.html b/testing/gallery/index.html
index 444151c..6954023 100644
--- a/testing/gallery/index.html
+++ b/testing/gallery/index.html
@@ -42,27 +42,22 @@
 			</div>
 	
             <div class="col-4 col-md-3 col-lg-2 float-left p-md-2 p-lg-3">
-                <img class="box border border-gray box-shadow width-fit" src="_thumbnail/2021-01-02 23.51.34.jpg" alt="2021-01-02 23.51.34.mp4" onclick="changePicture(2);displayModal(true);">
-                <span class="px-2 pb-2 width-fit css-truncate css-truncate-target">2021-01-02 23.51.34.mp4</span>
-			</div>
-	
-            <div class="col-4 col-md-3 col-lg-2 float-left p-md-2 p-lg-3">
-                <img class="box border border-gray box-shadow width-fit" src="_thumbnail/2021-02-22 15.36.43-1.jpg" alt="2021-02-22 15.36.43-1.heic" onclick="changePicture(3);displayModal(true);">
+                <img class="box border border-gray box-shadow width-fit" src="_thumbnail/2021-02-22 15.36.43-1.jpg" alt="2021-02-22 15.36.43-1.heic" onclick="changePicture(2);displayModal(true);">
                 <span class="px-2 pb-2 width-fit css-truncate css-truncate-target">2021-02-22 15.36.43-1.heic</span>
 			</div>
 	
             <div class="col-4 col-md-3 col-lg-2 float-left p-md-2 p-lg-3">
-                <img class="box border border-gray box-shadow width-fit" src="_thumbnail/2021-02-25 15.40.44.jpg" alt="2021-02-25 15.40.44.png" onclick="changePicture(4);displayModal(true);">
+                <img class="box border border-gray box-shadow width-fit" src="_thumbnail/2021-02-25 15.40.44.jpg" alt="2021-02-25 15.40.44.png" onclick="changePicture(3);displayModal(true);">
                 <span class="px-2 pb-2 width-fit css-truncate css-truncate-target">2021-02-25 15.40.44.png</span>
 			</div>
 	
             <div class="col-4 col-md-3 col-lg-2 float-left p-md-2 p-lg-3">
-                <img class="box border border-gray box-shadow width-fit" src="_thumbnail/_DSC9363_DxO.jpg" alt="_DSC9363_DxO.jpg" onclick="changePicture(5);displayModal(true);">
+                <img class="box border border-gray box-shadow width-fit" src="_thumbnail/_DSC9363_DxO.jpg" alt="_DSC9363_DxO.jpg" onclick="changePicture(4);displayModal(true);">
                 <span class="px-2 pb-2 width-fit css-truncate css-truncate-target">_DSC9363_DxO.jpg</span>
 			</div>
 	
             <div class="col-4 col-md-3 col-lg-2 float-left p-md-2 p-lg-3">
-                <img class="box border border-gray box-shadow width-fit" src="_thumbnail/_DSC9439.jpg" alt="_DSC9439.jpg" onclick="changePicture(6);displayModal(true);">
+                <img class="box border border-gray box-shadow width-fit" src="_thumbnail/_DSC9439.jpg" alt="_DSC9439.jpg" onclick="changePicture(5);displayModal(true);">
                 <span class="px-2 pb-2 width-fit css-truncate css-truncate-target">_DSC9439.jpg</span>
 			</div>
 	
@@ -116,14 +111,6 @@
 		filename: "2021-01-01 17.11.35.heic"
 	}
 	
-	,
-	{
-		thumbnail: "_thumbnail/2021-01-02 23.51.34.jpg",
-		fullsize: "_fullsize/2021-01-02 23.51.34.mp4",
-		original: "_original/2021-01-02 23.51.34.mp4",
-		filename: "2021-01-02 23.51.34.mp4"
-	}
-	
 	,
 	{
 		thumbnail: "_thumbnail/2021-02-22 15.36.43-1.jpg",