diff --git a/pom.xml b/pom.xml
index aba49b34..1478d8c3 100644
--- a/pom.xml
+++ b/pom.xml
@@ -14,7 +14,7 @@
 		<project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
 		
 		<!-- Transkribus components' version numbers -->
-		<fimagestoreClient.version>0.4.1</fimagestoreClient.version>
+		<fimagestoreClient.version>0.4.2-SNAPSHOT</fimagestoreClient.version>
 		<pdfUtils.version>0.0.3</pdfUtils.version>
 		<interfaces.version>0.0.5</interfaces.version>
 	</properties>
diff --git a/src/main/java/eu/transkribus/core/io/util/ImgFileFilter.java b/src/main/java/eu/transkribus/core/io/util/ImgFileFilter.java
index 777e3fb2..785be14c 100644
--- a/src/main/java/eu/transkribus/core/io/util/ImgFileFilter.java
+++ b/src/main/java/eu/transkribus/core/io/util/ImgFileFilter.java
@@ -14,6 +14,6 @@ public boolean accept(File pathname) {
 		final String mime = MimeTypes.getMimeType(FilenameUtils.getExtension(pathname.getName()));
 		//is allowed mimetype and not starts with ".", which may occur on mac
 		//FIXME pathname.isFile() does not have to be checked here?
-		return pathname.isFile() && !pathname.getName().startsWith(".") && ImgPriority.priorities.containsKey(mime);
+		return pathname.isFile() && !pathname.getName().startsWith(".") && ImgPriority.containsMimeType(mime);
 	}
 }
diff --git a/src/main/java/eu/transkribus/core/io/util/ImgFilenameFilter.java b/src/main/java/eu/transkribus/core/io/util/ImgFilenameFilter.java
index 839d8bcb..91ec251f 100644
--- a/src/main/java/eu/transkribus/core/io/util/ImgFilenameFilter.java
+++ b/src/main/java/eu/transkribus/core/io/util/ImgFilenameFilter.java
@@ -12,7 +12,7 @@ public class ImgFilenameFilter implements FilenameFilter {
 	public boolean accept(File dir, String name) {
 		final String mime = MimeTypes.getMimeType(FilenameUtils.getExtension(name));
 		//is allowed mimetype and not starts with ".", which may occur on mac
-		return !name.startsWith(".") && ImgPriority.priorities.containsKey(mime);
+		return !name.startsWith(".") && ImgPriority.containsMimeType(mime);
 	}
 
 }
diff --git a/src/main/java/eu/transkribus/core/io/util/ImgPriority.java b/src/main/java/eu/transkribus/core/io/util/ImgPriority.java
index 49073657..5709c8f6 100644
--- a/src/main/java/eu/transkribus/core/io/util/ImgPriority.java
+++ b/src/main/java/eu/transkribus/core/io/util/ImgPriority.java
@@ -1,15 +1,21 @@
 package eu.transkribus.core.io.util;
 
 import java.io.File;
+import java.util.ArrayList;
 import java.util.HashMap;
+import java.util.List;
 import java.util.Map;
 
 import org.apache.commons.io.FilenameUtils;
 import org.dea.fimagestore.core.util.MimeTypes;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
 
 public class ImgPriority {
+	private static final Logger logger = LoggerFactory.getLogger(ImgPriority.class);
+	
 	// this map will be used to prioritize different images for one page on the path
-	public static Map<String, Integer> priorities = new HashMap<>();
+	private static Map<String, Integer> priorities = new HashMap<>();
 
 	static {
 		//jpg > tif/tiff
@@ -22,4 +28,24 @@ public static Integer getPriority(File f) {
 		final String mime = MimeTypes.getMimeType(FilenameUtils.getExtension(f.getName()));
 		return priorities.get(mime);
 	}
+	
+	public static boolean containsMimeType(final String mimeType) {
+		return priorities.containsKey(mimeType);
+	}
+	
+	public static List<String> getAllowedFilenameExtensions() {
+		List<String> exts = new ArrayList<>(ImgPriority.priorities.size() * 2);
+		for(String mimeType : ImgPriority.priorities.keySet()) {
+			List<String> extsForType = MimeTypes.lookupExtensions(mimeType);
+			if(extsForType.isEmpty()) {
+				logger.error("Reverse lookup of registered mimetype failed: " + mimeType);
+				continue;
+			}
+			for(String ext : extsForType) {
+				exts.add(ext.toLowerCase());
+				exts.add(ext.toUpperCase());
+			}
+		}
+		return exts;
+	}
 }
diff --git a/src/test/java/eu/transkribus/core/io/util/ImgPriorityTest.java b/src/test/java/eu/transkribus/core/io/util/ImgPriorityTest.java
new file mode 100644
index 00000000..efab7d30
--- /dev/null
+++ b/src/test/java/eu/transkribus/core/io/util/ImgPriorityTest.java
@@ -0,0 +1,22 @@
+package eu.transkribus.core.io.util;
+
+import java.util.List;
+import java.util.stream.Collectors;
+
+import org.junit.Assert;
+import org.junit.Test;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+public class ImgPriorityTest {
+	private static final Logger logger = LoggerFactory.getLogger(ImgPriorityTest.class);
+	
+	@Test
+	public void testGetAllowedFilenameExtensions() {
+		List<String> exts = ImgPriority.getAllowedFilenameExtensions();
+		Assert.assertNotNull(exts);
+		logger.debug("Collected allowed file extensions: " + exts.stream().collect(Collectors.joining(", ")));
+		Assert.assertFalse(exts.isEmpty());
+	}
+
+}